/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */
package com.nulldev.util.internal.backport.concurrency9.concurrent;

import java.lang.Thread.UncaughtExceptionHandler;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.Permission;
import java.security.Permissions;
import java.security.PrivilegedAction;
import java.security.ProtectionDomain;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
import java.util.concurrent.AbstractExecutorService;
import java.util.concurrent.Callable;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.RunnableFuture;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;
import java.util.function.Predicate;

import com.nulldev.util.internal.unsafecompat.IUnsafe;

/**
 * An {@link ExecutorService} for running {@link ForkJoinTask}s. A
 * {@code ForkJoinPool} provides the entry point for submissions from
 * non-{@code ForkJoinTask} clients, as well as management and monitoring
 * operations.
 *
 * <p>
 * A {@code ForkJoinPool} differs from other kinds of {@link ExecutorService}
 * mainly by virtue of employing <em>work-stealing</em>: all threads in the pool
 * attempt to find and execute tasks submitted to the pool and/or created by
 * other active tasks (eventually blocking waiting for work if none exist). This
 * enables efficient processing when most tasks spawn other subtasks (as do most
 * {@code ForkJoinTask}s), as well as when many small tasks are submitted to the
 * pool from external clients. Especially when setting <em>asyncMode</em> to
 * true in constructors, {@code
 * ForkJoinPool}s may also be appropriate for use with event-style tasks that
 * are never joined. All worker threads are initialized with
 * {@link Thread#isDaemon} set {@code true}.
 *
 * <p>
 * A static {@link #commonPool()} is available and appropriate for most
 * applications. The common pool is used by any ForkJoinTask that is not
 * explicitly submitted to a specified pool. Using the common pool normally
 * reduces resource usage (its threads are slowly reclaimed during periods of
 * non-use, and reinstated upon subsequent use).
 *
 * <p>
 * For applications that require separate or custom pools, a {@code
 * ForkJoinPool} may be constructed with a given target parallelism level; by
 * default, equal to the number of available processors. The pool attempts to
 * maintain enough active (or available) threads by dynamically adding,
 * suspending, or resuming internal worker threads, even if some tasks are
 * stalled waiting to join others. However, no such adjustments are guaranteed
 * in the face of blocked I/O or other unmanaged synchronization. The nested
 * {@link ManagedBlocker} interface enables extension of the kinds of
 * synchronization accommodated. The default policies may be overridden using a
 * constructor with parameters corresponding to those documented in class
 * {@link ThreadPoolExecutor}.
 *
 * <p>
 * In addition to execution and lifecycle control methods, this class provides
 * status check methods (for example {@link #getStealCount}) that are intended
 * to aid in developing, tuning, and monitoring fork/join applications. Also,
 * method {@link #toString} returns indications of pool state in a convenient
 * form for informal monitoring.
 *
 * <p>
 * As is the case with other ExecutorServices, there are three main task
 * execution methods summarized in the following table. These are designed to be
 * used primarily by clients not already engaged in fork/join computations in
 * the current pool. The main forms of these methods accept instances of
 * {@code ForkJoinTask}, but overloaded forms also allow mixed execution of
 * plain {@code
 * Runnable}- or {@code Callable}- based activities as well. However, tasks that
 * are already executing in a pool should normally instead use the
 * within-computation forms listed in the table unless using async event-style
 * tasks that are not usually joined, in which case there is little difference
 * among choice of methods.
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1> <caption>Summary of task execution
 * methods</caption>
 * <tr>
 * <td></td>
 * <th scope="col">Call from non-fork/join clients</th>
 * <th scope="col">Call from within fork/join computations</th>
 * </tr>
 * <tr>
 * <th scope="row" style="text-align:left">Arrange async execution</th>
 * <td>{@link #execute(ForkJoinTask)}</td>
 * <td>{@link ForkJoinTask#fork}</td>
 * </tr>
 * <tr>
 * <th scope="row" style="text-align:left">Await and obtain result</th>
 * <td>{@link #invoke(ForkJoinTask)}</td>
 * <td>{@link ForkJoinTask#invoke}</td>
 * </tr>
 * <tr>
 * <th scope="row" style="text-align:left">Arrange exec and obtain Future</th>
 * <td>{@link #submit(ForkJoinTask)}</td>
 * <td>{@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
 * </tr>
 * </table>
 *
 * <p>
 * The parameters used to construct the common pool may be controlled by setting
 * the following {@linkplain System#getProperty system properties}:
 * <ul>
 * <li>{@code java.util.concurrent.ForkJoinPool.common.parallelism} - the
 * parallelism level, a non-negative integer
 * <li>{@code java.util.concurrent.ForkJoinPool.common.threadFactory} - the
 * class name of a {@link ForkJoinWorkerThreadFactory}. The
 * {@linkplain ClassLoader#getSystemClassLoader() system class loader} is used
 * to load this class.
 * <li>{@code java.util.concurrent.ForkJoinPool.common.exceptionHandler} - the
 * class name of a {@link UncaughtExceptionHandler}. The
 * {@linkplain ClassLoader#getSystemClassLoader() system class loader} is used
 * to load this class.
 * <li>{@code java.util.concurrent.ForkJoinPool.common.maximumSpares} - the
 * maximum number of allowed extra threads to maintain target parallelism
 * (default 256).
 * </ul>
 * If no thread factory is supplied via a system property, then the common pool
 * uses a factory that uses the system class loader as the
 * {@linkplain Thread#getContextClassLoader() thread context class loader}. In
 * addition, if a {@link SecurityManager} is present, then the common pool uses
 * a factory supplying threads that have no {@link Permissions} enabled.
 * 
 * Upon any error in establishing these settings, default parameters are used.
 * It is possible to disable or limit the use of threads in the common pool by
 * setting the parallelism property to zero, and/or using a factory that may
 * return {@code null}. However doing so may cause unjoined tasks to never be
 * executed.
 *
 * <p>
 * <b>Implementation Note:</b> This implementation restricts the maximum number
 * of running threads to 32767. Attempts to create pools with greater than the
 * maximum number result in {@code IllegalArgumentException}.
 *
 * <p>
 * This implementation rejects submitted tasks (that is, by throwing
 * {@link RejectedExecutionException}) only when the pool is shut down or
 * internal resources have been exhausted.
 *
 * @since 1.7
 * @author Doug Lea
 */
public class ForkJoinPool extends AbstractExecutorService {
// CVS rev. 1.344
	/*
	 * Implementation Overview
	 *
	 * This class and its nested classes provide the main functionality and control
	 * for a set of worker threads: Submissions from non-FJ threads enter into
	 * submission queues. Workers take these tasks and typically split them into
	 * subtasks that may be stolen by other workers. Preference rules give first
	 * priority to processing tasks from their own queues (LIFO or FIFO, depending
	 * on mode), then to randomized FIFO steals of tasks in other queues. This
	 * framework began as vehicle for supporting tree-structured parallelism using
	 * work-stealing. Over time, its scalability advantages led to extensions and
	 * changes to better support more diverse usage contexts. Because most internal
	 * methods and nested classes are interrelated, their main rationale and
	 * descriptions are presented here; individual methods and nested classes
	 * contain only brief comments about details.
	 *
	 * WorkQueues ==========
	 *
	 * Most operations occur within work-stealing queues (in nested class
	 * WorkQueue). These are special forms of Deques that support only three of the
	 * four possible end-operations -- push, pop, and poll (aka steal), under the
	 * further constraints that push and pop are called only from the owning thread
	 * (or, as extended here, under a lock), while poll may be called from other
	 * threads. (If you are unfamiliar with them, you probably want to read Herlihy
	 * and Shavit's book "The Art of Multiprocessor programming", chapter 16
	 * describing these in more detail before proceeding.) The main work-stealing
	 * queue design is roughly similar to those in the papers "Dynamic Circular
	 * Work-Stealing Deque" by Chase and Lev, SPAA 2005
	 * (http://research.sun.com/scalable/pubs/index.html) and
	 * "Idempotent work stealing" by Michael, Saraswat, and Vechev, PPoPP 2009
	 * (http://portal.acm.org/citation.cfm?id=1504186). The main differences
	 * ultimately stem from GC requirements that we null out taken slots as soon as
	 * we can, to maintain as small a footprint as possible even in programs
	 * generating huge numbers of tasks. To accomplish this, we shift the CAS
	 * arbitrating pop vs poll (steal) from being on the indices ("base" and "top")
	 * to the slots themselves.
	 *
	 * Adding tasks then takes the form of a classic array push(task) in a circular
	 * buffer: q.array[q.top++ % length] = task;
	 *
	 * (The actual code needs to null-check and size-check the array, uses masking,
	 * not mod, for indexing a power-of-two-sized array, properly fences accesses,
	 * and possibly signals waiting workers to start scanning -- see below.) Both a
	 * successful pop and poll mainly entail a CAS of a slot from non-null to null.
	 *
	 * The pop operation (always performed by owner) is: if ((the task at top slot
	 * is not null) and (CAS slot to null)) decrement top and return task;
	 *
	 * And the poll operation (usually by a stealer) is if ((the task at base slot
	 * is not null) and (CAS slot to null)) increment base and return task;
	 *
	 * There are several variants of each of these. In particular, almost all uses
	 * of poll occur within scan operations that also interleave contention tracking
	 * (with associated code sprawl.)
	 *
	 * Memory ordering. See "Correct and Efficient Work-Stealing for Weak Memory
	 * Models" by Le, Pop, Cohen, and Nardelli, PPoPP 2013
	 * (http://www.di.ens.fr/~zappa/readings/ppopp13.pdf) for an analysis of memory
	 * ordering requirements in work-stealing algorithms similar to (but different
	 * than) the one used here. Extracting tasks in array slots via (fully fenced)
	 * CAS provides primary synchronization. The base and top indices imprecisely
	 * guide where to extract from. We do not always require strict orderings of
	 * array and index updates, so sometimes let them be subject to compiler and
	 * processor reorderings. However, the volatile "base" index also serves as a
	 * basis for memory ordering: Slot accesses are preceded by a read of base,
	 * ensuring happens-before ordering with respect to stealers (so the slots
	 * themselves can be read via plain array reads.) The only other memory
	 * orderings relied on are maintained in the course of signalling and activation
	 * (see below). A check that base == top indicates (momentary) emptiness, but
	 * otherwise may err on the side of possibly making the queue appear nonempty
	 * when a push, pop, or poll have not fully committed, or making it appear empty
	 * when an update of top has not yet been visibly written. (Method isEmpty()
	 * checks the case of a partially completed removal of the last element.)
	 * Because of this, the poll operation, considered individually, is not
	 * wait-free. One thief cannot successfully continue until another in-progress
	 * one (or, if previously empty, a push) visibly completes. However, in the
	 * aggregate, we ensure at least probabilistic non-blockingness. If an attempted
	 * steal fails, a scanning thief chooses a different random victim target to try
	 * next. So, in order for one thief to progress, it suffices for any in-progress
	 * poll or new push on any empty queue to complete.
	 *
	 * This approach also enables support of a user mode in which local task
	 * processing is in FIFO, not LIFO order, simply by using poll rather than pop.
	 * This can be useful in message-passing frameworks in which tasks are never
	 * joined.
	 *
	 * WorkQueues are also used in a similar way for tasks submitted to the pool. We
	 * cannot mix these tasks in the same queues used by workers. Instead, we
	 * randomly associate submission queues with submitting threads, using a form of
	 * hashing. The ThreadLocalRandom probe value serves as a hash code for choosing
	 * existing queues, and may be randomly repositioned upon contention with other
	 * submitters. In essence, submitters act like workers except that they are
	 * restricted to executing local tasks that they submitted. Insertion of tasks
	 * in shared mode requires a lock but we use only a simple spinlock (using field
	 * phase), because submitters encountering a busy queue move to a different
	 * position to use or create other queues -- they block only when creating and
	 * registering new queues. Because it is used only as a spinlock, unlocking
	 * requires only a "releasing" store (using putOrderedInt).
	 *
	 * Management ==========
	 *
	 * The main throughput advantages of work-stealing stem from decentralized
	 * control -- workers mostly take tasks from themselves or each other, at rates
	 * that can exceed a billion per second. The pool itself creates, activates
	 * (enables scanning for and running tasks), deactivates, blocks, and terminates
	 * threads, all with minimal central information. There are only a few
	 * properties that we can globally track or maintain, so we pack them into a
	 * small number of variables, often maintaining atomicity without blocking or
	 * locking. Nearly all essentially atomic control state is held in a few
	 * volatile variables that are by far most often read (not written) as status
	 * and consistency checks. We pack as much information into them as we can.
	 *
	 * Field "ctl" contains 64 bits holding information needed to atomically decide
	 * to add, enqueue (on an event queue), and dequeue (and release)-activate
	 * workers. To enable this packing, we restrict maximum parallelism to (1<<15)-1
	 * (which is far in excess of normal operating range) to allow ids, counts, and
	 * their negations (used for thresholding) to fit into 16bit subfields.
	 *
	 * Field "mode" holds configuration parameters as well as lifetime status,
	 * atomically and monotonically setting SHUTDOWN, STOP, and finally TERMINATED
	 * bits.
	 *
	 * Field "workQueues" holds references to WorkQueues. It is updated (only during
	 * worker creation and termination) under lock (using field workerNamePrefix as
	 * lock), but is otherwise concurrently readable, and accessed directly. We also
	 * ensure that uses of the array reference itself never become too stale in case
	 * of resizing. To simplify index-based operations, the array size is always a
	 * power of two, and all readers must tolerate null slots. Worker queues are at
	 * odd indices. Shared (submission) queues are at even indices, up to a maximum
	 * of 64 slots, to limit growth even if array needs to expand to add more
	 * workers. Grouping them together in this way simplifies and speeds up task
	 * scanning.
	 *
	 * All worker thread creation is on-demand, triggered by task submissions,
	 * replacement of terminated workers, and/or compensation for blocked workers.
	 * However, all other support code is set up to work with other policies. To
	 * ensure that we do not hold on to worker references that would prevent GC, all
	 * accesses to workQueues are via indices into the workQueues array (which is
	 * one source of some of the messy code constructions here). In essence, the
	 * workQueues array serves as a weak reference mechanism. Thus for example the
	 * stack top subfield of ctl stores indices, not references.
	 *
	 * Queuing Idle Workers. Unlike HPC work-stealing frameworks, we cannot let
	 * workers spin indefinitely scanning for tasks when none can be found
	 * immediately, and we cannot start/resume workers unless there appear to be
	 * tasks available. On the other hand, we must quickly prod them into action
	 * when new tasks are submitted or generated. In many usages, ramp-up time is
	 * the main limiting factor in overall performance, which is compounded at
	 * program start-up by JIT compilation and allocation. So we streamline this as
	 * much as possible.
	 *
	 * The "ctl" field atomically maintains total worker and "released" worker
	 * counts, plus the head of the available worker queue (actually stack,
	 * represented by the lower 32bit subfield of ctl). Released workers are those
	 * known to be scanning for and/or running tasks. Unreleased ("available")
	 * workers are recorded in the ctl stack. These workers are made available for
	 * signalling by enqueuing in ctl (see method runWorker). The "queue" is a form
	 * of Treiber stack. This is ideal for activating threads in most-recently used
	 * order, and improves performance and locality, outweighing the disadvantages
	 * of being prone to contention and inability to release a worker unless it is
	 * topmost on stack. To avoid missed signal problems inherent in any wait/signal
	 * design, available workers rescan for (and if found run) tasks after
	 * enqueuing. Normally their release status will be updated while doing so, but
	 * the released worker ctl count may underestimate the number of active threads.
	 * (However, it is still possible to determine quiescence via a validation
	 * traversal -- see isQuiescent). After an unsuccessful rescan, available
	 * workers are blocked until signalled (see signalWork). The top stack state
	 * holds the value of the "phase" field of the worker: its index and status,
	 * plus a version counter that, in addition to the count subfields (also serving
	 * as version stamps) provide protection against Treiber stack ABA effects.
	 *
	 * Creating workers. To create a worker, we pre-increment counts (serving as a
	 * reservation), and attempt to construct a ForkJoinWorkerThread via its
	 * factory. Upon construction, the new thread invokes registerWorker, where it
	 * constructs a WorkQueue and is assigned an index in the workQueues array
	 * (expanding the array if necessary). The thread is then started. Upon any
	 * exception across these steps, or null return from factory, deregisterWorker
	 * adjusts counts and records accordingly. If a null return, the pool continues
	 * running with fewer than the target number workers. If exceptional, the
	 * exception is propagated, generally to some external caller. Worker index
	 * assignment avoids the bias in scanning that would occur if entries were
	 * sequentially packed starting at the front of the workQueues array. We treat
	 * the array as a simple power-of-two hash table, expanding as needed. The
	 * seedIndex increment ensures no collisions until a resize is needed or a
	 * worker is deregistered and replaced, and thereafter keeps probability of
	 * collision low. We cannot use ThreadLocalRandom.getProbe() for similar
	 * purposes here because the thread has not started yet, but do so for creating
	 * submission queues for existing external threads (see externalPush).
	 *
	 * WorkQueue field "phase" is used by both workers and the pool to manage and
	 * track whether a worker is UNSIGNALLED (possibly blocked waiting for a
	 * signal). When a worker is enqueued its phase field is set. Note that phase
	 * field updates lag queue CAS releases so usage requires care -- seeing a
	 * negative phase does not guarantee that the worker is available. When queued,
	 * the lower 16 bits of scanState must hold its pool index. So we place the
	 * index there upon initialization (see registerWorker) and otherwise keep it
	 * there or restore it when necessary.
	 *
	 * The ctl field also serves as the basis for memory synchronization surrounding
	 * activation. This uses a more efficient version of a Dekker-like rule that
	 * task producers and consumers sync with each other by both writing/CASing ctl
	 * (even if to its current value). This would be extremely costly. So we relax
	 * it in several ways: (1) Producers only signal when their queue is empty.
	 * Other workers propagate this signal (in method scan) when they find tasks; to
	 * further reduce flailing, each worker signals only one other per activation.
	 * (2) Workers only enqueue after scanning (see below) and not finding any
	 * tasks. (3) Rather than CASing ctl to its current value in the common case
	 * where no action is required, we reduce write contention by equivalently
	 * prefacing signalWork when called by an external task producer using a memory
	 * access with full-volatile semantics or a "fullFence".
	 *
	 * Almost always, too many signals are issued. A task producer cannot in general
	 * tell if some existing worker is in the midst of finishing one task (or
	 * already scanning) and ready to take another without being signalled. So the
	 * producer might instead activate a different worker that does not find any
	 * work, and then inactivates. This scarcely matters in steady-state
	 * computations involving all workers, but can create contention and bookkeeping
	 * bottlenecks during ramp-up, ramp-down, and small computations involving only
	 * a few workers.
	 *
	 * Scanning. Method runWorker performs top-level scanning for tasks. Each scan
	 * traverses and tries to poll from each queue starting at a random index and
	 * circularly stepping. Scans are not performed in ideal random permutation
	 * order, to reduce cacheline contention. The pseudorandom generator need not
	 * have high-quality statistical properties in the long term, but just within
	 * computations; We use Marsaglia XorShifts (often via
	 * ThreadLocalRandom.nextSecondarySeed), which are cheap and suffice. Scanning
	 * also employs contention reduction: When scanning workers fail to extract an
	 * apparently existing task, they soon restart at a different pseudorandom
	 * index. This improves throughput when many threads are trying to take tasks
	 * from few queues, which can be common in some usages. Scans do not otherwise
	 * explicitly take into account core affinities, loads, cache localities, etc,
	 * However, they do exploit temporal locality (which usually approximates these)
	 * by preferring to re-poll (at most #workers times) from the same queue after a
	 * successful poll before trying others.
	 *
	 * Trimming workers. To release resources after periods of lack of use, a worker
	 * starting to wait when the pool is quiescent will time out and terminate (see
	 * method scan) if the pool has remained quiescent for period given by field
	 * keepAlive.
	 *
	 * Shutdown and Termination. A call to shutdownNow invokes tryTerminate to
	 * atomically set a runState bit. The calling thread, as well as every other
	 * worker thereafter terminating, helps terminate others by cancelling their
	 * unprocessed tasks, and waking them up, doing so repeatedly until stable.
	 * Calls to non-abrupt shutdown() preface this by checking whether termination
	 * should commence by sweeping through queues (until stable) to ensure lack of
	 * in-flight submissions and workers about to process them before triggering the
	 * "STOP" phase of termination.
	 *
	 * Joining Tasks =============
	 *
	 * Any of several actions may be taken when one worker is waiting to join a task
	 * stolen (or always held) by another. Because we are multiplexing many tasks on
	 * to a pool of workers, we can't always just let them block (as in
	 * Thread.join). We also cannot just reassign the joiner's run-time stack with
	 * another and replace it later, which would be a form of "continuation", that
	 * even if possible is not necessarily a good idea since we may need both an
	 * unblocked task and its continuation to progress. Instead we combine two
	 * tactics:
	 *
	 * Helping: Arranging for the joiner to execute some task that it would be
	 * running if the steal had not occurred.
	 *
	 * Compensating: Unless there are already enough live threads, method
	 * tryCompensate() may create or re-activate a spare thread to compensate for
	 * blocked joiners until they unblock.
	 *
	 * A third form (implemented in tryRemoveAndExec) amounts to helping a
	 * hypothetical compensator: If we can readily tell that a possible action of a
	 * compensator is to steal and execute the task being joined, the joining thread
	 * can do so directly, without the need for a compensation thread.
	 *
	 * The ManagedBlocker extension API can't use helping so relies only on
	 * compensation in method awaitBlocker.
	 *
	 * The algorithm in awaitJoin entails a form of "linear helping". Each worker
	 * records (in field source) the id of the queue from which it last stole a
	 * task. The scan in method awaitJoin uses these markers to try to find a worker
	 * to help (i.e., steal back a task from and execute it) that could hasten
	 * completion of the actively joined task. Thus, the joiner executes a task that
	 * would be on its own local deque if the to-be-joined task had not been stolen.
	 * This is a conservative variant of the approach described in Wagner & Calder
	 * "Leapfrogging: a portable technique for implementing efficient futures"
	 * SIGPLAN Notices, 1993 (http://portal.acm.org/citation.cfm?id=155354). It
	 * differs mainly in that we only record queue ids, not full dependency links.
	 * This requires a linear scan of the workQueues array to locate stealers, but
	 * isolates cost to when it is needed, rather than adding to per-task overhead.
	 * Searches can fail to locate stealers GC stalls and the like delay recording
	 * sources. Further, even when accurately identified, stealers might not ever
	 * produce a task that the joiner can in turn help with. So, compensation is
	 * tried upon failure to find tasks to run.
	 *
	 * Compensation does not by default aim to keep exactly the target parallelism
	 * number of unblocked threads running at any given time. Some previous versions
	 * of this class employed immediate compensations for any blocked join. However,
	 * in practice, the vast majority of blockages are transient byproducts of GC
	 * and other JVM or OS activities that are made worse by replacement. Rather
	 * than impose arbitrary policies, we allow users to override the default of
	 * only adding threads upon apparent starvation. The compensation mechanism may
	 * also be bounded. Bounds for the commonPool (see COMMON_MAX_SPARES) better
	 * enable JVMs to cope with programming errors and abuse before running out of
	 * resources to do so.
	 *
	 * Common Pool ===========
	 *
	 * The static common pool always exists after static initialization. Since it
	 * (or any other created pool) need never be used, we minimize initial
	 * construction overhead and footprint to the setup of about a dozen fields.
	 *
	 * When external threads submit to the common pool, they can perform subtask
	 * processing (see externalHelpComplete and related methods) upon joins. This
	 * caller-helps policy makes it sensible to set common pool parallelism level to
	 * one (or more) less than the total number of available cores, or even zero for
	 * pure caller-runs. We do not need to record whether external submissions are
	 * to the common pool -- if not, external help methods return quickly. These
	 * submitters would otherwise be blocked waiting for completion, so the extra
	 * effort (with liberally sprinkled task status checks) in inapplicable cases
	 * amounts to an odd form of limited spin-wait before blocking in
	 * ForkJoinTask.join.
	 *
	 * As a more appropriate default in managed environments, unless overridden by
	 * system properties, we use workers of subclass InnocuousForkJoinWorkerThread
	 * when there is a SecurityManager present. These workers have no permissions
	 * set, do not belong to any user-defined ThreadGroup, and erase all
	 * ThreadLocals after executing any top-level task (see
	 * WorkQueue.afterTopLevelExec). The associated mechanics (mainly in
	 * ForkJoinWorkerThread) may be JVM-dependent and must access particular Thread
	 * class fields to achieve this effect.
	 *
	 * Style notes ===========
	 *
	 * Memory ordering relies mainly on Unsafe intrinsics that carry the further
	 * responsibility of explicitly performing null- and bounds- checks otherwise
	 * carried out implicitly by JVMs. This can be awkward and ugly, but also
	 * reflects the need to control outcomes across the unusual cases that arise in
	 * very racy code with very few invariants. All fields are read into locals
	 * before use, and null-checked if they are references. This is usually done in
	 * a "C"-like style of listing declarations at the heads of methods or blocks,
	 * and using inline assignments on first encounter. Nearly all explicit checks
	 * lead to bypass/return, not exception throws, because they may legitimately
	 * arise due to cancellation/revocation during shutdown.
	 *
	 * There is a lot of representation-level coupling among classes ForkJoinPool,
	 * ForkJoinWorkerThread, and ForkJoinTask. The fields of WorkQueue maintain data
	 * structures managed by ForkJoinPool, so are directly accessed. There is little
	 * point trying to reduce this, since any associated future changes in
	 * representations will need to be accompanied by algorithmic changes anyway.
	 * Several methods intrinsically sprawl because they must accumulate sets of
	 * consistent reads of fields held in local variables. There are also other
	 * coding oddities (including several unnecessary-looking hoisted null checks)
	 * that help some methods perform reasonably even when interpreted (not
	 * compiled).
	 *
	 * The order of declarations in this file is (with a few exceptions): (1) Static
	 * utility functions (2) Nested (static) classes (3) Static fields (4) Fields,
	 * along with constants used when unpacking some of them (5) Internal control
	 * methods (6) Callbacks and other support for ForkJoinTask methods (7) Exported
	 * methods (8) Static block initializing statics in minimally dependent order
	 */

	// Static utilities

	/**
	 * If there is a security manager, makes sure caller has permission to modify
	 * threads.
	 */
	private static void checkPermission() {
		SecurityManager security = System.getSecurityManager();
		if (security != null)
			security.checkPermission(modifyThreadPermission);
	}

	// Nested classes

	/**
	 * Factory for creating new {@link ForkJoinWorkerThread}s. A
	 * {@code ForkJoinWorkerThreadFactory} must be defined and used for
	 * {@code ForkJoinWorkerThread} subclasses that extend base functionality or
	 * initialize threads with different contexts.
	 */
	public static interface ForkJoinWorkerThreadFactory {
		/**
		 * Returns a new worker thread operating in the given pool. Returning null or
		 * throwing an exception may result in tasks never being executed. If this
		 * method throws an exception, it is relayed to the caller of the method (for
		 * example {@code execute}) causing attempted thread creation. If this method
		 * returns null or throws an exception, it is not retried until the next
		 * attempted creation (for example another call to {@code execute}).
		 *
		 * @param pool the pool this thread works in
		 * @return the new worker thread, or {@code null} if the request to create a
		 *         thread is rejected
		 * @throws NullPointerException if the pool is null
		 */
		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
	}

	static AccessControlContext contextWithPermissions(Permission... perms) {
		Permissions permissions = new Permissions();
		for (Permission perm : perms)
			permissions.add(perm);
		return new AccessControlContext(new ProtectionDomain[]
			{ new ProtectionDomain(null, permissions) });
	}

	/**
	 * Default ForkJoinWorkerThreadFactory implementation; creates a new
	 * ForkJoinWorkerThread using the system class loader as the thread context
	 * class loader.
	 */
	private static final class DefaultForkJoinWorkerThreadFactory implements ForkJoinWorkerThreadFactory {
		private static final AccessControlContext ACC = contextWithPermissions(
//            new RuntimePermission("setContextClassLoader"), // java9-concurrent-backport changed
				new RuntimePermission("getClassLoader"));

		public final ForkJoinWorkerThread newThread(ForkJoinPool pool) {
			return AccessController.doPrivileged(new PrivilegedAction<ForkJoinWorkerThread>() {
				public ForkJoinWorkerThread run() {
					return new ForkJoinWorkerThread(pool, ClassLoader.getSystemClassLoader());
				}
			}, ACC);
		}
	}

	// Constants shared across ForkJoinPool and WorkQueue

	// Bounds
	static final int SWIDTH = 16; // width of short
	static final int SMASK = 0xffff; // short bits == max index
	protected static final int MAX_CAP = 0x7fff; // max #workers - 1
	static final int SQMASK = 0x007e; // max 64 (even) slots

	// Masks and units for WorkQueue.phase and ctl sp subfield
	static final int UNSIGNALLED = 1 << 31; // must be negative
	static final int SS_SEQ = 1 << 16; // version count
	static final int QLOCK = 1; // must be 1

	// Mode bits and sentinels, some also used in WorkQueue id and.source fields
	static final int OWNED = 1; // queue has owner thread
	static final int FIFO = 1 << 16; // fifo queue or access mode
	static final int SHUTDOWN = 1 << 18;
	static final int TERMINATED = 1 << 19;
	static final int STOP = 1 << 31; // must be negative
	static final int QUIET = 1 << 30; // not scanning or working
	static final int DORMANT = QUIET | UNSIGNALLED;

	/**
	 * The maximum number of local polls from the same queue before checking others.
	 * This is a safeguard against infinitely unfair looping under unbounded user
	 * task recursion, and must be larger than plausible cases of intentional
	 * bounded task recursion.
	 */
	static final int POLL_LIMIT = 1 << 10;

	/**
	 * Queues supporting work-stealing as well as external task submission. See
	 * above for descriptions and algorithms. Performance on most platforms is very
	 * sensitive to placement of instances of both WorkQueues and their arrays -- we
	 * absolutely do not want multiple WorkQueue instances or multiple queue arrays
	 * sharing cache lines.
	 */
	// For now, using manual padding.
	static final class WorkQueue {

		/**
		 * Capacity of work-stealing queue array upon initialization. Must be a power of
		 * two; at least 4, but should be larger to reduce or eliminate cacheline
		 * sharing among queues. Currently, it is much larger, as a partial workaround
		 * for the fact that JVMs often place arrays in locations that share GC
		 * bookkeeping (especially cardmarks) such that per-write accesses encounter
		 * serious memory contention.
		 */
		static final int INITIAL_QUEUE_CAPACITY = 1 << 13;

		/**
		 * Maximum size for queue arrays. Must be a power of two less than or equal to 1
		 * << (31 - width of array entry) to ensure lack of wraparound of index
		 * calculations, but defined to a value a bit less than this to help users trap
		 * runaway programs before saturating systems.
		 */
		static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M

		// Instance fields
		volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06, pad07;
		volatile long pad08, pad09, pad0a, pad0b, pad0c, pad0d, pad0e, pad0f;
		volatile int phase; // versioned, negative: queued, 1: locked
		int stackPred; // pool stack (ctl) predecessor link
		int nsteals; // number of steals
		int id; // index, mode, tag
		volatile int source; // source queue id, or sentinel
		volatile int base; // index of next slot for poll
		int top; // index of next slot for push
		ForkJoinTask<?>[] array; // the elements (initially unallocated)
		final ForkJoinPool pool; // the containing pool (may be null)
		final ForkJoinWorkerThread owner; // owning thread or null if shared
		volatile Object pad10, pad11, pad12, pad13, pad14, pad15, pad16, pad17;
		volatile Object pad18, pad19, pad1a, pad1b, pad1c, pad1d, pad1e, pad1f;

		WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner) {
			this.pool = pool;
			this.owner = owner;
			// Place indices in the center of array (that is not yet allocated)
			base = top = INITIAL_QUEUE_CAPACITY >>> 1;
		}

		/**
		 * Returns an exportable index (used by ForkJoinWorkerThread).
		 */
		final int getPoolIndex() {
			return (id & 0xffff) >>> 1; // ignore odd/even tag bit
		}

		/**
		 * Returns the approximate number of tasks in the queue.
		 */
		final int queueSize() {
			int n = base - top; // read base first
			return (n >= 0) ? 0 : -n; // ignore transient negative
		}

		/**
		 * Provides a more accurate estimate of whether this queue has any tasks than
		 * does queueSize, by checking whether a near-empty queue has at least one
		 * unclaimed task.
		 */
		final boolean isEmpty() {
			ForkJoinTask<?>[] a;
			int n, al, b;
			return ((n = (b = base) - top) >= 0 || // possibly one task
					(n == -1 && ((a = array) == null || (al = a.length) == 0 || a[(al - 1) & b] == null)));
		}

		/**
		 * Pushes a task. Call only by owner in unshared queues.
		 *
		 * @param task the task. Caller must ensure non-null.
		 * @throws RejectedExecutionException if array cannot be resized
		 */
		final void push(ForkJoinTask<?> task) {
			int s = top;
			ForkJoinTask<?>[] a;
			int al, d;
			if ((a = array) != null && (al = a.length) > 0) {
				int index = (al - 1) & s;
				long offset = ((long) index << ASHIFT) + ABASE;
				ForkJoinPool p = pool;
				top = s + 1;
				U.putOrderedObject(a, offset, task);
				if ((d = base - s) == 0 && p != null) {
					U.fullFence();
					p.signalWork();
				} else if (d + al == 1)
					growArray();
			}
		}

		/**
		 * Initializes or doubles the capacity of array. Call either by owner or with
		 * lock held -- it is OK for base, but not top, to move while resizings are in
		 * progress.
		 */
		final ForkJoinTask<?>[] growArray() {
			ForkJoinTask<?>[] oldA = array;
			int oldSize = oldA != null ? oldA.length : 0;
			int size = oldSize > 0 ? oldSize << 1 : INITIAL_QUEUE_CAPACITY;
			if (size < INITIAL_QUEUE_CAPACITY || size > MAXIMUM_QUEUE_CAPACITY)
				throw new RejectedExecutionException("Queue capacity exceeded");
			int oldMask, t, b;
			ForkJoinTask<?>[] a = array = new ForkJoinTask<?>[size];
			if (oldA != null && (oldMask = oldSize - 1) > 0 && (t = top) - (b = base) > 0) {
				int mask = size - 1;
				do { // emulate poll from old array, push to new array
					int index = b & oldMask;
					long offset = ((long) index << ASHIFT) + ABASE;
					ForkJoinTask<?> x = (ForkJoinTask<?>) U.getObjectVolatile(oldA, offset);
					if (x != null && U.compareAndSwapObject(oldA, offset, x, null))
						a[b & mask] = x;
				} while (++b != t);
				U.storeFence();
			}
			return a;
		}

		/**
		 * Takes next task, if one exists, in LIFO order. Call only by owner in unshared
		 * queues.
		 */
		final ForkJoinTask<?> pop() {
			int b = base, s = top, al;
			ForkJoinTask<?>[] a;
			if ((a = array) != null && b != s && (al = a.length) > 0) {
				int index = (al - 1) & --s;
				long offset = ((long) index << ASHIFT) + ABASE;
				ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObject(a, offset);
				if (t != null && U.compareAndSwapObject(a, offset, t, null)) {
					top = s;
					U.storeFence();
					return t;
				}
			}
			return null;
		}

		/**
		 * Takes next task, if one exists, in FIFO order.
		 */
		final ForkJoinTask<?> poll() {
			for (;;) {
				int b = base, s = top, d, al;
				ForkJoinTask<?>[] a;
				if ((a = array) != null && (d = b - s) < 0 && (al = a.length) > 0) {
					int index = (al - 1) & b;
					long offset = ((long) index << ASHIFT) + ABASE;
					ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObjectVolatile(a, offset);
					if (b++ == base) {
						if (t != null) {
							if (U.compareAndSwapObject(a, offset, t, null)) {
								base = b;
								return t;
							}
						} else if (d == -1)
							break; // now empty
					}
				} else
					break;
			}
			return null;
		}

		/**
		 * Takes next task, if one exists, in order specified by mode.
		 */
		final ForkJoinTask<?> nextLocalTask() {
			return ((id & FIFO) != 0) ? poll() : pop();
		}

		/**
		 * Returns next task, if one exists, in order specified by mode.
		 */
		final ForkJoinTask<?> peek() {
			int al;
			ForkJoinTask<?>[] a;
			return ((a = array) != null && (al = a.length) > 0) ? a[(al - 1) & ((id & FIFO) != 0 ? base : top - 1)] : null;
		}

		/**
		 * Pops the given task only if it is at the current top.
		 */
		final boolean tryUnpush(ForkJoinTask<?> task) {
			int b = base, s = top, al;
			ForkJoinTask<?>[] a;
			if ((a = array) != null && b != s && (al = a.length) > 0) {
				int index = (al - 1) & --s;
				long offset = ((long) index << ASHIFT) + ABASE;
				if (U.compareAndSwapObject(a, offset, task, null)) {
					top = s;
					U.storeFence();
					return true;
				}
			}
			return false;
		}

		/**
		 * Removes and cancels all known tasks, ignoring any exceptions.
		 */
		final void cancelAll() {
			for (ForkJoinTask<?> t; (t = poll()) != null;)
				ForkJoinTask.cancelIgnoringExceptions(t);
		}

		// Specialized execution methods

		/**
		 * Pops and executes up to limit consecutive tasks or until empty.
		 *
		 * @param limit max runs, or zero for no limit
		 */
		final void localPopAndExec(int limit) {
			for (;;) {
				int b = base, s = top, al;
				ForkJoinTask<?>[] a;
				if ((a = array) != null && b != s && (al = a.length) > 0) {
					int index = (al - 1) & --s;
					long offset = ((long) index << ASHIFT) + ABASE;
					ForkJoinTask<?> t = (ForkJoinTask<?>) U.getAndSetObject(a, offset, null);
					if (t != null) {
						top = s;
						U.storeFence();
						t.doExec();
						if (limit != 0 && --limit == 0)
							break;
					} else
						break;
				} else
					break;
			}
		}

		/**
		 * Polls and executes up to limit consecutive tasks or until empty.
		 *
		 * @param limit, or zero for no limit
		 */
		final void localPollAndExec(int limit) {
			for (int polls = 0;;) {
				int b = base, s = top, d, al;
				ForkJoinTask<?>[] a;
				if ((a = array) != null && (d = b - s) < 0 && (al = a.length) > 0) {
					int index = (al - 1) & b++;
					long offset = ((long) index << ASHIFT) + ABASE;
					ForkJoinTask<?> t = (ForkJoinTask<?>) U.getAndSetObject(a, offset, null);
					if (t != null) {
						base = b;
						t.doExec();
						if (limit != 0 && ++polls == limit)
							break;
					} else if (d == -1)
						break; // now empty
					else
						polls = 0; // stolen; reset
				} else
					break;
			}
		}

		/**
		 * If present, removes task from queue and executes it.
		 */
		final void tryRemoveAndExec(ForkJoinTask<?> task) {
			ForkJoinTask<?>[] wa;
			int s, wal;
			if (base - (s = top) < 0 && // traverse from top
					(wa = array) != null && (wal = wa.length) > 0) {
				for (int m = wal - 1, ns = s - 1, i = ns;; --i) {
					int index = i & m;
					long offset = (index << ASHIFT) + ABASE;
					ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObject(wa, offset);
					if (t == null)
						break;
					else if (t == task) {
						if (U.compareAndSwapObject(wa, offset, t, null)) {
							top = ns; // safely shift down
							for (int j = i; j != ns; ++j) {
								ForkJoinTask<?> f;
								int pindex = (j + 1) & m;
								long pOffset = (pindex << ASHIFT) + ABASE;
								f = (ForkJoinTask<?>) U.getObject(wa, pOffset);
								U.putObjectVolatile(wa, pOffset, null);

								int jindex = j & m;
								long jOffset = (jindex << ASHIFT) + ABASE;
								U.putOrderedObject(wa, jOffset, f);
							}
							U.storeFence();
							t.doExec();
						}
						break;
					}
				}
			}
		}

		/**
		 * Tries to steal and run tasks within the target's computation until done, not
		 * found, or limit exceeded.
		 *
		 * @param task  root of CountedCompleter computation
		 * @param limit max runs, or zero for no limit
		 * @return task status on exit
		 */
		final int localHelpCC(CountedCompleter<?> task, int limit) {
			int status = 0;
			if (task != null && (status = task.status) >= 0) {
				for (;;) {
					boolean help = false;
					int b = base, s = top, al;
					ForkJoinTask<?>[] a;
					if ((a = array) != null && b != s && (al = a.length) > 0) {
						int index = (al - 1) & (s - 1);
						long offset = ((long) index << ASHIFT) + ABASE;
						ForkJoinTask<?> o = (ForkJoinTask<?>) U.getObject(a, offset);
						if (o instanceof CountedCompleter) {
							CountedCompleter<?> t = (CountedCompleter<?>) o;
							for (CountedCompleter<?> f = t;;) {
								if (f != task) {
									if ((f = f.completer) == null) // try parent
										break;
								} else {
									if (U.compareAndSwapObject(a, offset, t, null)) {
										top = s - 1;
										U.storeFence();
										t.doExec();
										help = true;
									}
									break;
								}
							}
						}
					}
					if ((status = task.status) < 0 || !help || (limit != 0 && --limit == 0))
						break;
				}
			}
			return status;
		}

		// Operations on shared queues

		/**
		 * Tries to lock shared queue by CASing phase field.
		 */
		final boolean tryLockSharedQueue() {
			return U.compareAndSwapInt(this, PHASE, 0, QLOCK);
		}

		/**
		 * Shared version of tryUnpush.
		 */
		final boolean trySharedUnpush(ForkJoinTask<?> task) {
			boolean popped = false;
			int s = top - 1, al;
			ForkJoinTask<?>[] a;
			if ((a = array) != null && (al = a.length) > 0) {
				int index = (al - 1) & s;
				long offset = ((long) index << ASHIFT) + ABASE;
				ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObject(a, offset);
				if (t == task && U.compareAndSwapInt(this, PHASE, 0, QLOCK)) {
					if (top == s + 1 && array == a && U.compareAndSwapObject(a, offset, task, null)) {
						popped = true;
						top = s;
					}
					U.putOrderedInt(this, PHASE, 0);
				}
			}
			return popped;
		}

		/**
		 * Shared version of localHelpCC.
		 */
		final int sharedHelpCC(CountedCompleter<?> task, int limit) {
			int status = 0;
			if (task != null && (status = task.status) >= 0) {
				for (;;) {
					boolean help = false;
					int b = base, s = top, al;
					ForkJoinTask<?>[] a;
					if ((a = array) != null && b != s && (al = a.length) > 0) {
						int index = (al - 1) & (s - 1);
						long offset = ((long) index << ASHIFT) + ABASE;
						ForkJoinTask<?> o = (ForkJoinTask<?>) U.getObject(a, offset);
						if (o instanceof CountedCompleter) {
							CountedCompleter<?> t = (CountedCompleter<?>) o;
							for (CountedCompleter<?> f = t;;) {
								if (f != task) {
									if ((f = f.completer) == null)
										break;
								} else {
									if (U.compareAndSwapInt(this, PHASE, 0, QLOCK)) {
										if (top == s && array == a && U.compareAndSwapObject(a, offset, t, null)) {
											help = true;
											top = s - 1;
										}
										U.putOrderedInt(this, PHASE, 0);
										if (help)
											t.doExec();
									}
									break;
								}
							}
						}
					}
					if ((status = task.status) < 0 || !help || (limit != 0 && --limit == 0))
						break;
				}
			}
			return status;
		}

		/**
		 * Returns true if owned and not known to be blocked.
		 */
		final boolean isApparentlyUnblocked() {
			Thread wt;
			Thread.State s;
			return ((wt = owner) != null && (s = wt.getState()) != Thread.State.BLOCKED && s != Thread.State.WAITING && s != Thread.State.TIMED_WAITING);
		}

		// Unsafe mechanics. Note that some are (and must be) the same as in FJP
		private static final IUnsafe U = UnsafeAccess.unsafe;
		private static final long PHASE;
		private static final int ABASE;
		private static final int ASHIFT;
		static {
			try {
				PHASE = U.objectFieldOffset(WorkQueue.class.getDeclaredField("phase"));
				ABASE = U.arrayBaseOffset(ForkJoinTask[].class);
				int scale = U.arrayIndexScale(ForkJoinTask[].class);
				if ((scale & (scale - 1)) != 0)
					throw new ExceptionInInitializerError("array index scale not a power of two");
				ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
			} catch (Exception e) {
				throw new ExceptionInInitializerError(e);
			}
		}
	}

	// static fields (initialized in static initializer below)

	/**
	 * Creates a new ForkJoinWorkerThread. This factory is used unless overridden in
	 * ForkJoinPool constructors.
	 */
	public static final ForkJoinWorkerThreadFactory defaultForkJoinWorkerThreadFactory;

	/**
	 * Permission required for callers of methods that may start or kill threads.
	 */
	static final RuntimePermission modifyThreadPermission;

	/**
	 * Common (static) pool. Non-null for public use unless a static construction
	 * exception, but internal usages null-check on use to paranoically avoid
	 * potential initialization circularities as well as to simplify generated code.
	 */
	static final ForkJoinPool common;

	/**
	 * Common pool parallelism. To allow simpler use and management when common pool
	 * threads are disabled, we allow the underlying common.parallelism field to be
	 * zero, but in that case still report parallelism as 1 to reflect resulting
	 * caller-runs mechanics.
	 */
	static final int COMMON_PARALLELISM;

	/**
	 * Limit on spare thread construction in tryCompensate.
	 */
	private static final int COMMON_MAX_SPARES;

	/**
	 * Sequence number for creating workerNamePrefix.
	 */
	private static int poolNumberSequence;

	/**
	 * Returns the next sequence number. We don't expect this to ever contend, so
	 * use simple builtin sync.
	 */
	private static final synchronized int nextPoolId() {
		return ++poolNumberSequence;
	}

	// static configuration constants

	/**
	 * Default idle timeout value (in milliseconds) for the thread triggering
	 * quiescence to park waiting for new work
	 */
	protected static final long DEFAULT_KEEPALIVE = 60_000L;

	/**
	 * Undershoot tolerance for idle timeouts
	 */
	private static final long TIMEOUT_SLOP = 20L;

	/**
	 * The default value for COMMON_MAX_SPARES. Overridable using the
	 * "java.util.concurrent.ForkJoinPool.common.maximumSpares" system property. The
	 * default value is far in excess of normal requirements, but also far short of
	 * MAX_CAP and typical OS thread limits, so allows JVMs to catch misuse/abuse
	 * before running out of resources needed to do so.
	 */
	private static final int DEFAULT_COMMON_MAX_SPARES = 256;

	/**
	 * Increment for seed generators. See class ThreadLocal for explanation.
	 */
	private static final int SEED_INCREMENT = 0x9e3779b9;

	/*
	 * Bits and masks for field ctl, packed with 4 16 bit subfields: RC: Number of
	 * released (unqueued) workers minus target parallelism TC: Number of total
	 * workers minus target parallelism SS: version count and status of top waiting
	 * thread ID: poolIndex of top of Treiber stack of waiters
	 *
	 * When convenient, we can extract the lower 32 stack top bits (including
	 * version bits) as sp=(int)ctl. The offsets of counts by the target parallelism
	 * and the positionings of fields makes it possible to perform the most common
	 * checks via sign tests of fields: When ac is negative, there are not enough
	 * unqueued workers, when tc is negative, there are not enough total workers.
	 * When sp is non-zero, there are waiting workers. To deal with possibly
	 * negative fields, we use casts in and out of "short" and/or signed shifts to
	 * maintain signedness.
	 *
	 * Because it occupies uppermost bits, we can add one release count using
	 * getAndAddLong of RC_UNIT, rather than CAS, when returning from a blocked
	 * join. Other updates entail multiple subfields and masking, requiring CAS.
	 *
	 * The limits packed in field "bounds" are also offset by the parallelism level
	 * to make them comparable to the ctl rc and tc fields.
	 */

	// Lower and upper word masks
	private static final long SP_MASK = 0xffffffffL;
	private static final long UC_MASK = ~SP_MASK;

	// Release counts
	private static final int RC_SHIFT = 48;
	private static final long RC_UNIT = 0x0001L << RC_SHIFT;
	private static final long RC_MASK = 0xffffL << RC_SHIFT;

	// Total counts
	private static final int TC_SHIFT = 32;
	private static final long TC_UNIT = 0x0001L << TC_SHIFT;
	private static final long TC_MASK = 0xffffL << TC_SHIFT;
	private static final long ADD_WORKER = 0x0001L << (TC_SHIFT + 15); // sign

	// Instance fields

	// Segregate ctl field, For now using padding vs @Contended
	volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06, pad07;
	volatile long pad08, pad09, pad0a, pad0b, pad0c, pad0d, pad0e, pad0f;
	volatile long ctl; // main pool control
	volatile long pad10, pad11, pad12, pad13, pad14, pad15, pad16, pad17;
	volatile long pad18, pad19, pad1a, pad1b, pad1c, pad1d, pad1e;

	volatile long stealCount; // collects worker nsteals
	final long keepAlive; // milliseconds before dropping if idle
	volatile int indexSeed; // next worker index
	final int bounds; // min, max threads packed as shorts
	volatile int mode; // parallelism, runstate, queue mode
	volatile WorkQueue[] workQueues; // main registry
	final String workerNamePrefix; // for worker thread string; sync lock
	final ForkJoinWorkerThreadFactory factory;
	final UncaughtExceptionHandler ueh; // per-worker UEH
	final Predicate<? super ForkJoinPool> saturate;

	// Creating, registering and deregistering workers

	/**
	 * Tries to construct and start one worker. Assumes that total count has already
	 * been incremented as a reservation. Invokes deregisterWorker on any failure.
	 *
	 * @return true if successful
	 */
	private boolean createWorker() {
		ForkJoinWorkerThreadFactory fac = factory;
		Throwable ex = null;
		ForkJoinWorkerThread wt = null;
		try {
			if (fac != null && (wt = fac.newThread(this)) != null) {
				wt.start();
				return true;
			}
		} catch (Throwable rex) {
			ex = rex;
		}
		deregisterWorker(wt, ex);
		return false;
	}

	/**
	 * Tries to add one worker, incrementing ctl counts before doing so, relying on
	 * createWorker to back out on failure.
	 *
	 * @param c incoming ctl value, with total count negative and no idle workers.
	 *          On CAS failure, c is refreshed and retried if this holds (otherwise,
	 *          a new worker is not needed).
	 */
	private void tryAddWorker(long c) {
		do {
			long nc = ((RC_MASK & (c + RC_UNIT)) | (TC_MASK & (c + TC_UNIT)));
			if (ctl == c && U.compareAndSwapLong(this, CTL, c, nc)) {
				createWorker();
				break;
			}
		} while (((c = ctl) & ADD_WORKER) != 0L && (int) c == 0);
	}

	/**
	 * Callback from ForkJoinWorkerThread constructor to establish and record its
	 * WorkQueue.
	 *
	 * @param wt the worker thread
	 * @return the worker's queue
	 */
	final WorkQueue registerWorker(ForkJoinWorkerThread wt) {
		UncaughtExceptionHandler handler;
		wt.setDaemon(true); // configure thread
		if ((handler = ueh) != null)
			wt.setUncaughtExceptionHandler(handler);
		WorkQueue w = new WorkQueue(this, wt);
		int tid = 0; // for thread name
		int fifo = mode & FIFO;
		String prefix = workerNamePrefix;
		if (prefix != null) {
			synchronized (prefix) {
				WorkQueue[] ws = workQueues;
				int n;
				int s = indexSeed += SEED_INCREMENT;
				if (ws != null && (n = ws.length) > 1) {
					int m = n - 1;
					tid = s & m;
					int i = m & ((s << 1) | 1); // odd-numbered indices
					for (int probes = n >>> 1;;) { // find empty slot
						WorkQueue q;
						if ((q = ws[i]) == null || q.phase == QUIET)
							break;
						else if (--probes == 0) {
							i = n | 1; // resize below
							break;
						} else
							i = (i + 2) & m;
					}

					int id = i | fifo | (s & ~(SMASK | FIFO | DORMANT));
					w.phase = w.id = id; // now publishable

					if (i < n)
						ws[i] = w;
					else { // expand array
						int an = n << 1;
						WorkQueue[] as = new WorkQueue[an];
						as[i] = w;
						int am = an - 1;
						for (int j = 0; j < n; ++j) {
							WorkQueue v; // copy external queue
							if ((v = ws[j]) != null) // position may change
								as[v.id & am & SQMASK] = v;
							if (++j >= n)
								break;
							as[j] = ws[j]; // copy worker
						}
						workQueues = as;
					}
				}
			}
			wt.setName(prefix.concat(Integer.toString(tid)));
		}
		return w;
	}

	/**
	 * Final callback from terminating worker, as well as upon failure to construct
	 * or start a worker. Removes record of worker from array, and adjusts counts.
	 * If pool is shutting down, tries to complete termination.
	 *
	 * @param wt the worker thread, or null if construction failed
	 * @param ex the exception causing failure, or null if none
	 */
	final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
		WorkQueue w = null;
		int phase = 0;
		if (wt != null && (w = wt.workQueue) != null) {
			Object lock = workerNamePrefix;
			long ns = (long) w.nsteals & 0xffffffffL;
			int idx = w.id & SMASK;
			if (lock != null) {
				WorkQueue[] ws; // remove index from array
				synchronized (lock) {
					if ((ws = workQueues) != null && ws.length > idx && ws[idx] == w)
						ws[idx] = null;
					stealCount += ns;
				}
			}
			phase = w.phase;
		}
		if (phase != QUIET) { // else pre-adjusted
			long c; // decrement counts
			do {
			} while (!U.compareAndSwapLong(this, CTL, c = ctl, ((RC_MASK & (c - RC_UNIT)) | (TC_MASK & (c - TC_UNIT)) | (SP_MASK & c))));
		}
		if (w != null)
			w.cancelAll(); // cancel remaining tasks

		if (!tryTerminate(false, false) && // possibly replace worker
				w != null && w.array != null) // avoid repeated failures
			signalWork();

		if (ex == null) // help clean on way out
			ForkJoinTask.helpExpungeStaleExceptions();
		else // rethrow
			ForkJoinTask.rethrow(ex);
	}

	/**
	 * Tries to create or release a worker if too few are running.
	 */
	final void signalWork() {
		for (;;) {
			long c;
			int sp;
			WorkQueue[] ws;
			int i;
			WorkQueue v;
			if ((c = ctl) >= 0L) // enough workers
				break;
			else if ((sp = (int) c) == 0) { // no idle workers
				if ((c & ADD_WORKER) != 0L) // too few workers
					tryAddWorker(c);
				break;
			} else if ((ws = workQueues) == null)
				break; // unstarted/terminated
			else if (ws.length <= (i = sp & SMASK))
				break; // terminated
			else if ((v = ws[i]) == null)
				break; // terminating
			else {
				int np = sp & ~UNSIGNALLED;
				int vp = v.phase;
				long nc = (v.stackPred & SP_MASK) | (UC_MASK & (c + RC_UNIT));
				Thread vt = v.owner;
				if (sp == vp && U.compareAndSwapLong(this, CTL, c, nc)) {
					v.phase = np;
					if (v.source < 0)
						LockSupport.unpark(vt);
					break;
				}
			}
		}
	}

	/**
	 * Tries to decrement counts (sometimes implicitly) and possibly arrange for a
	 * compensating worker in preparation for blocking: If not all core workers yet
	 * exist, creates one, else if any are unreleased (possibly including caller)
	 * releases one, else if fewer than the minimum allowed number of workers
	 * running, checks to see that they are all active, and if so creates an extra
	 * worker unless over maximum limit and policy is to saturate. Most of these
	 * steps can fail due to interference, in which case 0 is returned so caller
	 * will retry. A negative return value indicates that the caller doesn't need to
	 * re-adjust counts when later unblocked.
	 *
	 * @return 1: block then adjust, -1: block without adjust, 0 : retry
	 */
	private int tryCompensate(WorkQueue w) {
		int t, n, sp;
		long c = ctl;
		WorkQueue[] ws = workQueues;
		if ((t = (short) (c >>> TC_SHIFT)) >= 0) {
			if (ws == null || (n = ws.length) <= 0 || w == null)
				return 0; // disabled
			else if ((sp = (int) c) != 0) { // replace or release
				WorkQueue v = ws[sp & (n - 1)];
				int wp = w.phase;
				long uc = UC_MASK & ((wp < 0) ? c + RC_UNIT : c);
				int np = sp & ~UNSIGNALLED;
				if (v != null) {
					int vp = v.phase;
					Thread vt = v.owner;
					long nc = ((long) v.stackPred & SP_MASK) | uc;
					if (vp == sp && U.compareAndSwapLong(this, CTL, c, nc)) {
						v.phase = np;
						if (v.source < 0)
							LockSupport.unpark(vt);
						return (wp < 0) ? -1 : 1;
					}
				}
				return 0;
			} else if ((int) (c >> RC_SHIFT) - // reduce parallelism
					(short) (bounds & SMASK) > 0) {
				long nc = ((RC_MASK & (c - RC_UNIT)) | (~RC_MASK & c));
				return U.compareAndSwapLong(this, CTL, c, nc) ? 1 : 0;
			} else { // validate
				int md = mode, pc = md & SMASK, tc = pc + t, bc = 0;
				boolean unstable = false;
				for (int i = 1; i < n; i += 2) {
					WorkQueue q;
					Thread wt;
					Thread.State ts;
					if ((q = ws[i]) != null) {
						if (q.source == 0) {
							unstable = true;
							break;
						} else {
							--tc;
							if ((wt = q.owner) != null && ((ts = wt.getState()) == Thread.State.BLOCKED || ts == Thread.State.WAITING))
								++bc; // worker is blocking
						}
					}
				}
				if (unstable || tc != 0 || ctl != c)
					return 0; // inconsistent
				else if (t + pc >= MAX_CAP || t >= (bounds >>> SWIDTH)) {
					Predicate<? super ForkJoinPool> sat;
					if ((sat = saturate) != null && sat.test(this))
						return -1;
					else if (bc < pc) { // lagging
						Thread.yield(); // for retry spins
						return 0;
					} else
						throw new RejectedExecutionException("Thread limit exceeded replacing blocked worker");
				}
			}
		}

		long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK); // expand pool
		return U.compareAndSwapLong(this, CTL, c, nc) && createWorker() ? 1 : 0;
	}

	/**
	 * Top-level runloop for workers, called by ForkJoinWorkerThread.run. See above
	 * for explanation.
	 */
	final void runWorker(WorkQueue w) {
		WorkQueue[] ws;
		w.growArray(); // allocate queue
		int r = w.id ^ TLRandom.nextSecondarySeed();
		if (r == 0) // initial nonzero seed
			r = 1;
		int lastSignalId = 0; // avoid unneeded signals
		while ((ws = workQueues) != null) {
			boolean nonempty = false; // scan
			for (int n = ws.length, j = n, m = n - 1; j > 0; --j) {
				WorkQueue q;
				int i, b, al;
				ForkJoinTask<?>[] a;
				if ((i = r & m) >= 0 && i < n && // always true
						(q = ws[i]) != null && (b = q.base) - q.top < 0 && (a = q.array) != null && (al = a.length) > 0) {
					int qid = q.id; // (never zero)
					int index = (al - 1) & b;
					long offset = ((long) index << ASHIFT) + ABASE;
					ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObjectVolatile(a, offset);
					if (t != null && b++ == q.base && U.compareAndSwapObject(a, offset, t, null)) {
						if ((q.base = b) - q.top < 0 && qid != lastSignalId)
							signalWork(); // propagate signal
						w.source = lastSignalId = qid;
						t.doExec();
						if ((w.id & FIFO) != 0) // run remaining locals
							w.localPollAndExec(POLL_LIMIT);
						else
							w.localPopAndExec(POLL_LIMIT);
						ForkJoinWorkerThread thread = w.owner;
						++w.nsteals;
						w.source = 0; // now idle
						if (thread != null)
							thread.afterTopLevelExec();
					}
					nonempty = true;
				} else if (nonempty)
					break;
				else
					++r;
			}

			if (nonempty) { // move (xorshift)
				r ^= r << 13;
				r ^= r >>> 17;
				r ^= r << 5;
			} else {
				int phase;
				lastSignalId = 0; // clear for next scan
				if ((phase = w.phase) >= 0) { // enqueue
					int np = w.phase = (phase + SS_SEQ) | UNSIGNALLED;
					long c, nc;
					do {
						w.stackPred = (int) (c = ctl);
						nc = ((c - RC_UNIT) & UC_MASK) | (SP_MASK & np);
					} while (!U.compareAndSwapLong(this, CTL, c, nc));
				} else { // already queued
					int pred = w.stackPred;
					w.source = DORMANT; // enable signal
					for (int steps = 0;;) {
						int md, rc;
						long c;
						if (w.phase >= 0) {
							w.source = 0;
							break;
						} else if ((md = mode) < 0) // shutting down
							return;
						else if ((rc = ((md & SMASK) + // possibly quiescent
								(int) ((c = ctl) >> RC_SHIFT))) <= 0 && (md & SHUTDOWN) != 0 && tryTerminate(false, false))
							return; // help terminate
						else if ((++steps & 1) == 0)
							Thread.interrupted(); // clear between parks
						else if (rc <= 0 && pred != 0 && phase == (int) c) {
							long d = keepAlive + System.currentTimeMillis();
							LockSupport.parkUntil(this, d);
							if (ctl == c && d - System.currentTimeMillis() <= TIMEOUT_SLOP) {
								long nc = ((UC_MASK & (c - TC_UNIT)) | (SP_MASK & pred));
								if (U.compareAndSwapLong(this, CTL, c, nc)) {
									w.phase = QUIET;
									return; // drop on timeout
								}
							}
						} else
							LockSupport.park(this);
					}
				}
			}
		}
	}

	/**
	 * Helps and/or blocks until the given task is done or timeout. First tries
	 * locally helping, then scans other queues for a task produced by one of w's
	 * stealers; compensating and blocking if none are found (rescanning if
	 * tryCompensate fails).
	 *
	 * @param w        caller
	 * @param task     the task
	 * @param deadline for timed waits, if nonzero
	 * @return task status on exit
	 */
	final int awaitJoin(WorkQueue w, ForkJoinTask<?> task, long deadline) {
		int s = 0;
		if (w != null && task != null && (!(task instanceof CountedCompleter) || (s = w.localHelpCC((CountedCompleter<?>) task, 0)) >= 0)) {
			w.tryRemoveAndExec(task);
			int src = w.source, id = w.id;
			s = task.status;
			while (s >= 0) {
				WorkQueue[] ws;
				boolean nonempty = false;
				int r = TLRandom.nextSecondarySeed() | 1; // odd indices
				if ((ws = workQueues) != null) { // scan for matching id
					for (int n = ws.length, m = n - 1, j = -n; j < n; j += 2) {
						WorkQueue q;
						int i, b, al;
						ForkJoinTask<?>[] a;
						if ((i = (r + j) & m) >= 0 && i < n && (q = ws[i]) != null && q.source == id && (b = q.base) - q.top < 0 && (a = q.array) != null
								&& (al = a.length) > 0) {
							int qid = q.id;
							int index = (al - 1) & b;
							long offset = ((long) index << ASHIFT) + ABASE;
							ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObjectVolatile(a, offset);
							if (t != null && b++ == q.base && id == q.source && U.compareAndSwapObject(a, offset, t, null)) {
								q.base = b;
								w.source = qid;
								t.doExec();
								w.source = src;
							}
							nonempty = true;
							break;
						}
					}
				}
				if ((s = task.status) < 0)
					break;
				else if (!nonempty) {
					long ms, ns;
					int block;
					if (deadline == 0L)
						ms = 0L; // untimed
					else if ((ns = deadline - System.nanoTime()) <= 0L)
						break; // timeout
					else if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) <= 0L)
						ms = 1L; // avoid 0 for timed wait
					if ((block = tryCompensate(w)) != 0) {
						task.internalWait(ms);
						U.getAndAddLong(this, CTL, (block > 0) ? RC_UNIT : 0L);
					}
					s = task.status;
				}
			}
		}
		return s;
	}

	/**
	 * Runs tasks until {@code isQuiescent()}. Rather than blocking when tasks
	 * cannot be found, rescans until all others cannot find tasks either.
	 */
	final void helpQuiescePool(WorkQueue w) {
		int prevSrc = w.source, fifo = w.id & FIFO;
		for (int source = prevSrc, released = -1;;) { // -1 until known
			WorkQueue[] ws;
			if (fifo != 0)
				w.localPollAndExec(0);
			else
				w.localPopAndExec(0);
			if (released == -1 && w.phase >= 0)
				released = 1;
			boolean quiet = true, empty = true;
			int r = TLRandom.nextSecondarySeed();
			if ((ws = workQueues) != null) {
				for (int n = ws.length, j = n, m = n - 1; j > 0; --j) {
					WorkQueue q;
					int i, b, al;
					ForkJoinTask<?>[] a;
					if ((i = (r - j) & m) >= 0 && i < n && (q = ws[i]) != null) {
						if ((b = q.base) - q.top < 0 && (a = q.array) != null && (al = a.length) > 0) {
							if (released == 0) { // increment
								released = 1;
								U.getAndAddLong(this, CTL, RC_UNIT);
							}
							int index = (al - 1) & b;
							long offset = ((long) index << ASHIFT) + ABASE;
							ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObjectVolatile(a, offset);
							if (t != null && b++ == q.base && U.compareAndSwapObject(a, offset, t, null)) {
								q.base = b;
								w.source = source = q.id;
								t.doExec();
								w.source = source = prevSrc;
							}
							quiet = empty = false;
							break;
						} else if ((q.source & QUIET) == 0)
							quiet = false;
					}
				}
			}
			if (quiet) {
				if (released == 0)
					U.getAndAddLong(this, CTL, RC_UNIT);
				w.source = prevSrc;
				break;
			} else if (empty) {
				if (source != QUIET)
					w.source = source = QUIET;
				if (released == 1) { // decrement
					released = 0;
					U.getAndAddLong(this, CTL, RC_MASK & -RC_UNIT);
				}
			}
		}
	}

	/**
	 * Scans for and returns a polled task, if available. Used only for untracked
	 * polls.
	 *
	 * @param submissionsOnly if true, only scan submission queues
	 */
	private ForkJoinTask<?> pollScan(boolean submissionsOnly) {
		WorkQueue[] ws;
		int n;
		rescan: while ((mode & STOP) == 0 && (ws = workQueues) != null && (n = ws.length) > 0) {
			int m = n - 1;
			int r = TLRandom.nextSecondarySeed();
			int h = r >>> 16;
			int origin, step;
			if (submissionsOnly) {
				origin = (r & ~1) & m; // even indices and steps
				step = (h & ~1) | 2;
			} else {
				origin = r & m;
				step = h | 1;
			}
			for (int k = origin, oldSum = 0, checkSum = 0;;) {
				WorkQueue q;
				int b, al;
				ForkJoinTask<?>[] a;
				if ((q = ws[k]) != null) {
					checkSum += b = q.base;
					if (b - q.top < 0 && (a = q.array) != null && (al = a.length) > 0) {
						int index = (al - 1) & b;
						long offset = ((long) index << ASHIFT) + ABASE;
						ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObjectVolatile(a, offset);
						if (t != null && b++ == q.base && U.compareAndSwapObject(a, offset, t, null)) {
							q.base = b;
							return t;
						} else
							break; // restart
					}
				}
				if ((k = (k + step) & m) == origin) {
					if (oldSum == (oldSum = checkSum))
						break rescan;
					checkSum = 0;
				}
			}
		}
		return null;
	}

	/**
	 * Gets and removes a local or stolen task for the given worker.
	 *
	 * @return a task, if available
	 */
	final ForkJoinTask<?> nextTaskFor(WorkQueue w) {
		ForkJoinTask<?> t;
		if (w != null && (t = (w.id & FIFO) != 0 ? w.poll() : w.pop()) != null)
			return t;
		else
			return pollScan(false);
	}

	// External operations

	/**
	 * Adds the given task to a submission queue at submitter's current queue,
	 * creating one if null or contended.
	 *
	 * @param task the task. Caller must ensure non-null.
	 */
	final void externalPush(ForkJoinTask<?> task) {
		int r; // initialize caller's probe
		if ((r = TLRandom.getProbe()) == 0) {
			TLRandom.localInit();
			r = TLRandom.getProbe();
		}
		for (;;) {
			int md = mode, n;
			WorkQueue[] ws = workQueues;
			if ((md & SHUTDOWN) != 0 || ws == null || (n = ws.length) <= 0)
				throw new RejectedExecutionException();
			else {
				WorkQueue q;
				boolean push = false, grow = false;
				if ((q = ws[(n - 1) & r & SQMASK]) == null) {
					Object lock = workerNamePrefix;
					int qid = (r | QUIET) & ~(FIFO | OWNED);
					q = new WorkQueue(this, null);
					q.id = qid;
					q.source = QUIET;
					q.phase = QLOCK; // lock queue
					if (lock != null) {
						synchronized (lock) { // lock pool to install
							int i;
							if ((ws = workQueues) != null && (n = ws.length) > 0 && ws[i = qid & (n - 1) & SQMASK] == null) {
								ws[i] = q;
								push = grow = true;
							}
						}
					}
				} else if (q.tryLockSharedQueue()) {
					int b = q.base, s = q.top, al, d;
					ForkJoinTask<?>[] a;
					if ((a = q.array) != null && (al = a.length) > 0 && al - 1 + (d = b - s) > 0) {
						a[(al - 1) & s] = task;
						q.top = s + 1; // relaxed writes OK here
						q.phase = 0;
						if (d < 0 && q.base - s < -1)
							break; // no signal needed
					} else
						grow = true;
					push = true;
				}
				if (push) {
					if (grow) {
						try {
							q.growArray();
							int s = q.top, al;
							ForkJoinTask<?>[] a;
							if ((a = q.array) != null && (al = a.length) > 0) {
								a[(al - 1) & s] = task;
								q.top = s + 1;
							}
						} finally {
							q.phase = 0;
						}
					}
					signalWork();
					break;
				} else // move if busy
					r = TLRandom.advanceProbe(r);
			}
		}
	}

	/**
	 * Pushes a possibly-external submission.
	 */
	private <T> ForkJoinTask<T> externalSubmit(ForkJoinTask<T> task) {
		Thread t;
		ForkJoinWorkerThread w;
		WorkQueue q;
		Objects.requireNonNull(task);
		if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) && (w = (ForkJoinWorkerThread) t).pool == this && (q = w.workQueue) != null)
			q.push(task);
		else
			externalPush(task);
		return task;
	}

	/**
	 * Pushes a possibly-external submission.
	 */
	private <T> java.util.concurrent.ForkJoinTask<T> externalSubmit(final java.util.concurrent.ForkJoinTask<T> _task) {
		Thread t;
		ForkJoinWorkerThread w;
		WorkQueue q;
		Objects.requireNonNull(_task);
		final ForkJoinTask<?> task = submit(() -> {
			_task.quietlyInvoke();
		});
		if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) && (w = (ForkJoinWorkerThread) t).pool == this && (q = w.workQueue) != null)
			q.push(task);
		else
			externalPush(task);
		return _task;
	}

	/**
	 * Returns common pool queue for an external thread.
	 */
	static WorkQueue commonSubmitterQueue() {
		ForkJoinPool p = common;
		int r = TLRandom.getProbe();
		WorkQueue[] ws;
		int n;
		return (p != null && (ws = p.workQueues) != null && (n = ws.length) > 0) ? ws[(n - 1) & r & SQMASK] : null;
	}

	/**
	 * Performs tryUnpush for an external submitter.
	 */
	final boolean tryExternalUnpush(ForkJoinTask<?> task) {
		int r = TLRandom.getProbe();
		WorkQueue[] ws;
		WorkQueue w;
		int n;
		return ((ws = workQueues) != null && (n = ws.length) > 0 && (w = ws[(n - 1) & r & SQMASK]) != null && w.trySharedUnpush(task));
	}

	/**
	 * Performs helpComplete for an external submitter.
	 */
	final int externalHelpComplete(CountedCompleter<?> task, int maxTasks) {
		int r = TLRandom.getProbe();
		WorkQueue[] ws;
		WorkQueue w;
		int n;
		return ((ws = workQueues) != null && (n = ws.length) > 0 && (w = ws[(n - 1) & r & SQMASK]) != null) ? w.sharedHelpCC(task, maxTasks) : 0;
	}

	/**
	 * Tries to steal and run tasks within the target's computation. The maxTasks
	 * argument supports external usages; internal calls use zero, allowing
	 * unbounded steps (external calls trap non-positive values).
	 *
	 * @param w        caller
	 * @param maxTasks if non-zero, the maximum number of other tasks to run
	 * @return task status on exit
	 */
	final int helpComplete(WorkQueue w, CountedCompleter<?> task, int maxTasks) {
		return (w == null) ? 0 : w.localHelpCC(task, maxTasks);
	}

	/**
	 * Returns a cheap heuristic guide for task partitioning when programmers,
	 * frameworks, tools, or languages have little or no idea about task
	 * granularity. In essence, by offering this method, we ask users only about
	 * tradeoffs in overhead vs expected throughput and its variance, rather than
	 * how finely to partition tasks.
	 *
	 * In a steady state strict (tree-structured) computation, each thread makes
	 * available for stealing enough tasks for other threads to remain active.
	 * Inductively, if all threads play by the same rules, each thread should make
	 * available only a constant number of tasks.
	 *
	 * The minimum useful constant is just 1. But using a value of 1 would require
	 * immediate replenishment upon each steal to maintain enough tasks, which is
	 * infeasible. Further, partitionings/granularities of offered tasks should
	 * minimize steal rates, which in general means that threads nearer the top of
	 * computation tree should generate more than those nearer the bottom. In
	 * perfect steady state, each thread is at approximately the same level of
	 * computation tree. However, producing extra tasks amortizes the uncertainty of
	 * progress and diffusion assumptions.
	 *
	 * So, users will want to use values larger (but not much larger) than 1 to both
	 * smooth over transient shortages and hedge against uneven progress; as traded
	 * off against the cost of extra task overhead. We leave the user to pick a
	 * threshold value to compare with the results of this call to guide decisions,
	 * but recommend values such as 3.
	 *
	 * When all threads are active, it is on average OK to estimate surplus strictly
	 * locally. In steady-state, if one thread is maintaining say 2 surplus tasks,
	 * then so are others. So we can just use estimated queue length. However, this
	 * strategy alone leads to serious mis-estimates in some non-steady-state
	 * conditions (ramp-up, ramp-down, other stalls). We can detect many of these by
	 * further considering the number of "idle" threads, that are known to have zero
	 * queued tasks, so compensate by a factor of (#idle/#active) threads.
	 */
	static int getSurplusQueuedTaskCount() {
		Thread t;
		ForkJoinWorkerThread wt;
		ForkJoinPool pool;
		WorkQueue q;
		if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) && (pool = (wt = (ForkJoinWorkerThread) t).pool) != null
				&& (q = wt.workQueue) != null) {
			int p = pool.mode & SMASK;
			int a = p + (int) (pool.ctl >> RC_SHIFT);
			int n = q.top - q.base;
			return n - (a > (p >>>= 1) ? 0 : a > (p >>>= 1) ? 1 : a > (p >>>= 1) ? 2 : a > (p >>>= 1) ? 4 : 8);
		}
		return 0;
	}

	// Termination

	/**
	 * Possibly initiates and/or completes termination.
	 *
	 * @param now    if true, unconditionally terminate, else only if no work and no
	 *               active workers
	 * @param enable if true, terminate when next possible
	 * @return true if terminating or terminated
	 */
	private boolean tryTerminate(boolean now, boolean enable) {
		int md; // 3 phases: try to set SHUTDOWN, then STOP, then TERMINATED

		while (((md = mode) & SHUTDOWN) == 0) {
			if (!enable || this == common) // cannot shutdown
				return false;
			else
				U.compareAndSwapInt(this, MODE, md, md | SHUTDOWN);
		}

		while (((md = mode) & STOP) == 0) { // try to initiate termination
			if (!now) { // check if quiescent & empty
				for (long oldSum = 0L;;) { // repeat until stable
					boolean running = false;
					long checkSum = ctl;
					WorkQueue[] ws = workQueues;
					if ((md & SMASK) + (int) (checkSum >> RC_SHIFT) > 0)
						running = true;
					else if (ws != null) {
						WorkQueue w;
						for (int i = 0; i < ws.length; ++i) {
							if ((w = ws[i]) != null) {
								int s = w.source, p = w.phase;
								int d = w.id, b = w.base;
								if (b != w.top || ((d & 1) == 1 && (s >= 0 || p >= 0))) {
									running = true;
									break; // working, scanning, or have work
								}
								checkSum += (((long) s << 48) + ((long) p << 32) + ((long) b << 16) + (long) d);
							}
						}
					}
					if (((md = mode) & STOP) != 0)
						break; // already triggered
					else if (running)
						return false;
					else if (workQueues == ws && oldSum == (oldSum = checkSum))
						break;
				}
			}
			if ((md & STOP) == 0)
				U.compareAndSwapInt(this, MODE, md, md | STOP);
		}

		while (((md = mode) & TERMINATED) == 0) { // help terminate others
			for (long oldSum = 0L;;) { // repeat until stable
				WorkQueue[] ws;
				WorkQueue w;
				long checkSum = ctl;
				if ((ws = workQueues) != null) {
					for (int i = 0; i < ws.length; ++i) {
						if ((w = ws[i]) != null) {
							ForkJoinWorkerThread wt = w.owner;
							w.cancelAll(); // clear queues
							if (wt != null) {
								try { // unblock join or park
									wt.interrupt();
								} catch (Throwable ignore) {
								}
							}
							checkSum += ((long) w.phase << 32) + w.base;
						}
					}
				}
				if (((md = mode) & TERMINATED) != 0 || (workQueues == ws && oldSum == (oldSum = checkSum)))
					break;
			}
			if ((md & TERMINATED) != 0)
				break;
			else if ((md & SMASK) + (short) (ctl >>> TC_SHIFT) > 0)
				break;
			else if (U.compareAndSwapInt(this, MODE, md, md | TERMINATED)) {
				synchronized (this) {
					notifyAll(); // for awaitTermination
				}
				break;
			}
		}
		return true;
	}

	// Exported methods

	// Constructors

	/**
	 * Creates a {@code ForkJoinPool} with parallelism equal to
	 * {@link java.lang.Runtime#availableProcessors}, using defaults for all other
	 * parameters (see
	 * {@link #ForkJoinPool(int, ForkJoinWorkerThreadFactory, Thread.UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)}).
	 *
	 * @throws SecurityException if a security manager exists and the caller is not
	 *                           permitted to modify threads because it does not
	 *                           hold
	 *                           {@link java.lang.RuntimePermission}{@code ("modifyThread")}
	 */
	public ForkJoinPool() {
		this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()), defaultForkJoinWorkerThreadFactory, null, false, 0, MAX_CAP, 1, null,
				DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS);
	}

	/**
	 * Creates a {@code ForkJoinPool} with the indicated parallelism level, using
	 * defaults for all other parameters (see
	 * {@link #ForkJoinPool(int, ForkJoinWorkerThreadFactory, Thread.UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)}).
	 *
	 * @param parallelism the parallelism level
	 * @throws IllegalArgumentException if parallelism less than or equal to zero,
	 *                                  or greater than implementation limit
	 * @throws SecurityException        if a security manager exists and the caller
	 *                                  is not permitted to modify threads because
	 *                                  it does not hold
	 *                                  {@link java.lang.RuntimePermission}{@code ("modifyThread")}
	 */
	public ForkJoinPool(int parallelism) {
		this(parallelism, defaultForkJoinWorkerThreadFactory, null, false, 0, MAX_CAP, 1, null, DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS);
	}

	/**
	 * Creates a {@code ForkJoinPool} with the given parameters (using defaults for
	 * others -- see
	 * {@link #ForkJoinPool(int, ForkJoinWorkerThreadFactory, Thread.UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)}).
	 *
	 * @param parallelism the parallelism level. For default value, use
	 *                    {@link java.lang.Runtime#availableProcessors}.
	 * @param factory     the factory for creating new threads. For default value,
	 *                    use {@link #defaultForkJoinWorkerThreadFactory}.
	 * @param handler     the handler for internal worker threads that terminate due
	 *                    to unrecoverable errors encountered while executing tasks.
	 *                    For default value, use {@code null}.
	 * @param asyncMode   if true, establishes local first-in-first-out scheduling
	 *                    mode for forked tasks that are never joined. This mode may
	 *                    be more appropriate than default locally stack-based mode
	 *                    in applications in which worker threads only process
	 *                    event-style asynchronous tasks. For default value, use
	 *                    {@code false}.
	 * @throws IllegalArgumentException if parallelism less than or equal to zero,
	 *                                  or greater than implementation limit
	 * @throws NullPointerException     if the factory is null
	 * @throws SecurityException        if a security manager exists and the caller
	 *                                  is not permitted to modify threads because
	 *                                  it does not hold
	 *                                  {@link java.lang.RuntimePermission}{@code ("modifyThread")}
	 */
	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory, UncaughtExceptionHandler handler, boolean asyncMode) {
		this(parallelism, factory, handler, asyncMode, 0, MAX_CAP, 1, null, DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS);
	}

	/**
	 * Creates a {@code ForkJoinPool} with the given parameters.
	 *
	 * @param parallelism     the parallelism level. For default value, use
	 *                        {@link java.lang.Runtime#availableProcessors}.
	 *
	 * @param factory         the factory for creating new threads. For default
	 *                        value, use
	 *                        {@link #defaultForkJoinWorkerThreadFactory}.
	 *
	 * @param handler         the handler for internal worker threads that terminate
	 *                        due to unrecoverable errors encountered while
	 *                        executing tasks. For default value, use {@code null}.
	 *
	 * @param asyncMode       if true, establishes local first-in-first-out
	 *                        scheduling mode for forked tasks that are never
	 *                        joined. This mode may be more appropriate than default
	 *                        locally stack-based mode in applications in which
	 *                        worker threads only process event-style asynchronous
	 *                        tasks. For default value, use {@code
	 * false}              .
	 *
	 * @param corePoolSize    the number of threads to keep in the pool (unless
	 *                        timed out after an elapsed keep-alive). Normally (and
	 *                        by default) this is the same value as the parallelism
	 *                        level, but may be set to a larger value to reduce
	 *                        dynamic overhead if tasks regularly block. Using a
	 *                        smaller value (for example {@code 0}) has the same
	 *                        effect as the default.
	 *
	 * @param maximumPoolSize the maximum number of threads allowed. When the
	 *                        maximum is reached, attempts to replace blocked
	 *                        threads fail. (However, because creation and
	 *                        termination of different threads may overlap, and may
	 *                        be managed by the given thread factory, this value may
	 *                        be transiently exceeded.) To arrange the same value as
	 *                        is used by default for the common pool, use
	 *                        {@code 256} plus the {@code parallelism} level. (By
	 *                        default, the common pool allows a maximum of 256 spare
	 *                        threads.) Using a value (for example {@code
	 * Integer.MAX_VALUE}  ) larger than the implementation's total thread limit
	 *                        has the same effect as using this limit (which is the
	 *                        default).
	 *
	 * @param minimumRunnable the minimum allowed number of core threads not blocked
	 *                        by a join or {@link ManagedBlocker}. To ensure
	 *                        progress, when too few unblocked threads exist and
	 *                        unexecuted tasks may exist, new threads are
	 *                        constructed, up to the given maximumPoolSize. For the
	 *                        default value, use {@code
	 * 1}                  , that ensures liveness. A larger value might improve
	 *                        throughput in the presence of blocked activities, but
	 *                        might not, due to increased overhead. A value of zero
	 *                        may be acceptable when submitted tasks cannot have
	 *                        dependencies requiring additional threads.
	 *
	 * @param saturate        if non-null, a predicate invoked upon attempts to
	 *                        create more than the maximum total allowed threads. By
	 *                        default, when a thread is about to block on a join or
	 *                        {@link ManagedBlocker}, but cannot be replaced because
	 *                        the maximumPoolSize would be exceeded, a
	 *                        {@link RejectedExecutionException} is thrown. But if
	 *                        this predicate returns {@code true}, then no exception
	 *                        is thrown, so the pool continues to operate with fewer
	 *                        than the target number of runnable threads, which
	 *                        might not ensure progress.
	 *
	 * @param keepAliveTime   the elapsed time since last use before a thread is
	 *                        terminated (and then later replaced if needed). For
	 *                        the default value, use {@code 60, TimeUnit.SECONDS}.
	 *
	 * @param unit            the time unit for the {@code keepAliveTime} argument
	 *
	 * @throws IllegalArgumentException if parallelism is less than or equal to
	 *                                  zero, or is greater than implementation
	 *                                  limit, or if maximumPoolSize is less than
	 *                                  parallelism, of if the keepAliveTime is less
	 *                                  than or equal to zero.
	 * @throws NullPointerException     if the factory is null
	 * @throws SecurityException        if a security manager exists and the caller
	 *                                  is not permitted to modify threads because
	 *                                  it does not hold
	 *                                  {@link java.lang.RuntimePermission}{@code ("modifyThread")}
	 * @since 9
	 */
	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory, UncaughtExceptionHandler handler, boolean asyncMode, int corePoolSize,
			int maximumPoolSize, int minimumRunnable, Predicate<? super ForkJoinPool> saturate, long keepAliveTime, TimeUnit unit) {
		// check, encode, pack parameters
		if (parallelism <= 0 || parallelism > MAX_CAP || maximumPoolSize < parallelism || keepAliveTime <= 0L)
			throw new IllegalArgumentException();
		Objects.requireNonNull(factory);
		long ms = Math.max(unit.toMillis(keepAliveTime), TIMEOUT_SLOP);

		int corep = Math.min(Math.max(corePoolSize, parallelism), MAX_CAP);
		long c = ((((long) (-corep) << TC_SHIFT) & TC_MASK) | (((long) (-parallelism) << RC_SHIFT) & RC_MASK));
		int m = parallelism | (asyncMode ? FIFO : 0);
		int maxSpares = Math.min(maximumPoolSize, MAX_CAP) - parallelism;
		int minAvail = Math.min(Math.max(minimumRunnable, 0), MAX_CAP);
		int b = ((minAvail - parallelism) & SMASK) | (maxSpares << SWIDTH);
		int n = (parallelism > 1) ? parallelism - 1 : 1; // at least 2 slots
		n |= n >>> 1;
		n |= n >>> 2;
		n |= n >>> 4;
		n |= n >>> 8;
		n |= n >>> 16;
		n = (n + 1) << 1; // power of two, including space for submission queues

		this.workerNamePrefix = "ForkJoinPool-" + nextPoolId() + "-worker-";
		this.workQueues = new WorkQueue[n];
		this.factory = factory;
		this.ueh = handler;
		this.saturate = saturate;
		this.keepAlive = ms;
		this.bounds = b;
		this.mode = m;
		this.ctl = c;
		checkPermission();
	}

	private static Object newInstanceFromSystemProperty(String property) throws Exception {
		String className = System.getProperty(property);
		return (className == null) ? null : ClassLoader.getSystemClassLoader().loadClass(className).getConstructor().newInstance();
	}

	/**
	 * Constructor for common pool using parameters possibly overridden by system
	 * properties
	 */
	private ForkJoinPool(byte forCommonPoolOnly) {
		int parallelism = -1;
		ForkJoinWorkerThreadFactory fac = null;
		UncaughtExceptionHandler handler = null;
		try { // ignore exceptions in accessing/parsing properties
			String pp = System.getProperty("java.util.concurrent.ForkJoinPool.common.parallelism");
			if (pp != null)
				parallelism = Integer.parseInt(pp);
			fac = (ForkJoinWorkerThreadFactory) newInstanceFromSystemProperty("java.util.concurrent.ForkJoinPool.common.threadFactory");
			handler = (UncaughtExceptionHandler) newInstanceFromSystemProperty("java.util.concurrent.ForkJoinPool.common.exceptionHandler");
		} catch (Exception ignore) {
		}

		if (fac == null) {
			if (System.getSecurityManager() == null) {
				fac = defaultForkJoinWorkerThreadFactory;
			} else { // use security-managed default
				fac = new InnocuousForkJoinWorkerThreadFactory();
			}
		}
		if (parallelism < 0 && // default 1 less than #cores
				(parallelism = Runtime.getRuntime().availableProcessors() - 1) <= 0)
			parallelism = 1;
		if (parallelism > MAX_CAP)
			parallelism = MAX_CAP;

		long c = ((((long) (-parallelism) << TC_SHIFT) & TC_MASK) | (((long) (-parallelism) << RC_SHIFT) & RC_MASK));
		int b = ((1 - parallelism) & SMASK) | (COMMON_MAX_SPARES << SWIDTH);
		int n = (parallelism > 1) ? parallelism - 1 : 1;
		n |= n >>> 1;
		n |= n >>> 2;
		n |= n >>> 4;
		n |= n >>> 8;
		n |= n >>> 16;
		n = (n + 1) << 1;

		this.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
		this.workQueues = new WorkQueue[n];
		this.factory = fac;
		this.ueh = handler;
		this.saturate = null;
		this.keepAlive = DEFAULT_KEEPALIVE;
		this.bounds = b;
		this.mode = parallelism;
		this.ctl = c;
	}

	/**
	 * Returns the common pool instance. This pool is statically constructed; its
	 * run state is unaffected by attempts to {@link #shutdown} or
	 * {@link #shutdownNow}. However this pool and any ongoing processing are
	 * automatically terminated upon program {@link System#exit}. Any program that
	 * relies on asynchronous task processing to complete before program termination
	 * should invoke {@code commonPool().}{@link #awaitQuiescence awaitQuiescence},
	 * before exit.
	 *
	 * @return the common pool instance
	 * @since 1.8
	 */
	public static ForkJoinPool commonPool() {
		// assert common != null : "static init error";
		return common;
	}

	// Execution methods

	/**
	 * Performs the given task, returning its result upon completion. If the
	 * computation encounters an unchecked Exception or Error, it is rethrown as the
	 * outcome of this invocation. Rethrown exceptions behave in the same way as
	 * regular exceptions, but, when possible, contain stack traces (as displayed
	 * for example using {@code ex.printStackTrace()}) of both the current thread as
	 * well as the thread actually encountering the exception; minimally only the
	 * latter.
	 *
	 * @param task the task
	 * @param <T>  the type of the task's result
	 * @return the task's result
	 * @throws NullPointerException       if the task is null
	 * @throws RejectedExecutionException if the task cannot be scheduled for
	 *                                    execution
	 */
	public <T> T invoke(ForkJoinTask<T> task) {
		externalSubmit(Objects.requireNonNull(task));
		return task.join();
	}

	/**
	 * Arranges for (asynchronous) execution of the given task.
	 *
	 * @param task the task
	 * @throws NullPointerException       if the task is null
	 * @throws RejectedExecutionException if the task cannot be scheduled for
	 *                                    execution
	 */
	public void execute(ForkJoinTask<?> task) {
		externalSubmit(task);
	}

	public void execute(final java.util.concurrent.ForkJoinTask<?> task) {
		externalSubmit(task);
	}

	// AbstractExecutorService methods

	/**
	 * @throws NullPointerException       if the task is null
	 * @throws RejectedExecutionException if the task cannot be scheduled for
	 *                                    execution
	 */
	public void execute(Runnable task) {
		Objects.requireNonNull(task);
		ForkJoinTask<?> job;
		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
			job = (ForkJoinTask<?>) task;
		else
			job = new ForkJoinTask.RunnableExecuteAction(task);
		externalSubmit(job);
	}

	/**
	 * Submits a ForkJoinTask for execution.
	 *
	 * @param task the task to submit
	 * @param <T>  the type of the task's result
	 * @return the task
	 * @throws NullPointerException       if the task is null
	 * @throws RejectedExecutionException if the task cannot be scheduled for
	 *                                    execution
	 */
	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
		return externalSubmit(task);
	}

	/**
	 * @throws NullPointerException       if the task is null
	 * @throws RejectedExecutionException if the task cannot be scheduled for
	 *                                    execution
	 */
	public <T> ForkJoinTask<T> submit(Callable<T> task) {
		return externalSubmit(new ForkJoinTask.AdaptedCallable<T>(task));
	}

	/**
	 * @throws NullPointerException       if the task is null
	 * @throws RejectedExecutionException if the task cannot be scheduled for
	 *                                    execution
	 */
	public <T> ForkJoinTask<T> submit(Runnable task, T result) {
		return externalSubmit(new ForkJoinTask.AdaptedRunnable<T>(task, result));
	}

	/**
	 * @throws NullPointerException       if the task is null
	 * @throws RejectedExecutionException if the task cannot be scheduled for
	 *                                    execution
	 */
	@SuppressWarnings("unchecked")
	public ForkJoinTask<?> submit(Runnable task) {
		Objects.requireNonNull(task);
		return externalSubmit((task instanceof ForkJoinTask<?>) ? (ForkJoinTask<Void>) task // avoid re-wrap
				: new ForkJoinTask.AdaptedRunnableAction(task));
	}

	/**
	 * @throws NullPointerException       {@inheritDoc}
	 * @throws RejectedExecutionException {@inheritDoc}
	 */
	public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
		// In previous versions of this class, this method constructed
		// a task to run ForkJoinTask.invokeAll, but now external
		// invocation of multiple tasks is at least as efficient.
		ArrayList<Future<T>> futures = new ArrayList<>(tasks.size());

		try {
			for (Callable<T> t : tasks) {
				ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t);
				futures.add(f);
				externalSubmit(f);
			}
			for (int i = 0, size = futures.size(); i < size; i++)
				((ForkJoinTask<?>) futures.get(i)).quietlyJoin();
			return futures;
		} catch (Throwable t) {
			for (int i = 0, size = futures.size(); i < size; i++)
				futures.get(i).cancel(false);
			throw t;
		}
	}

	/**
	 * Returns the factory used for constructing new workers.
	 *
	 * @return the factory used for constructing new workers
	 */
	public ForkJoinWorkerThreadFactory getFactory() {
		return factory;
	}

	/**
	 * Returns the handler for internal worker threads that terminate due to
	 * unrecoverable errors encountered while executing tasks.
	 *
	 * @return the handler, or {@code null} if none
	 */
	public UncaughtExceptionHandler getUncaughtExceptionHandler() {
		return ueh;
	}

	/**
	 * Returns the targeted parallelism level of this pool.
	 *
	 * @return the targeted parallelism level of this pool
	 */
	public int getParallelism() {
		int par = mode & SMASK;
		return (par > 0) ? par : 1;
	}

	/**
	 * Returns the targeted parallelism level of the common pool.
	 *
	 * @return the targeted parallelism level of the common pool
	 * @since 1.8
	 */
	public static int getCommonPoolParallelism() {
		return COMMON_PARALLELISM;
	}

	/**
	 * Returns the number of worker threads that have started but not yet
	 * terminated. The result returned by this method may differ from
	 * {@link #getParallelism} when threads are created to maintain parallelism when
	 * others are cooperatively blocked.
	 *
	 * @return the number of worker threads
	 */
	public int getPoolSize() {
		return ((mode & SMASK) + (short) (ctl >>> TC_SHIFT));
	}

	/**
	 * Returns {@code true} if this pool uses local first-in-first-out scheduling
	 * mode for forked tasks that are never joined.
	 *
	 * @return {@code true} if this pool uses async mode
	 */
	public boolean getAsyncMode() {
		return (mode & FIFO) != 0;
	}

	/**
	 * Returns an estimate of the number of worker threads that are not blocked
	 * waiting to join tasks or for other managed synchronization. This method may
	 * overestimate the number of running threads.
	 *
	 * @return the number of worker threads
	 */
	public int getRunningThreadCount() {
		int rc = 0;
		WorkQueue[] ws;
		WorkQueue w;
		if ((ws = workQueues) != null) {
			for (int i = 1; i < ws.length; i += 2) {
				if ((w = ws[i]) != null && w.isApparentlyUnblocked())
					++rc;
			}
		}
		return rc;
	}

	/**
	 * Returns an estimate of the number of threads that are currently stealing or
	 * executing tasks. This method may overestimate the number of active threads.
	 *
	 * @return the number of active threads
	 */
	public int getActiveThreadCount() {
		int r = (mode & SMASK) + (int) (ctl >> RC_SHIFT);
		return (r <= 0) ? 0 : r; // suppress momentarily negative values
	}

	/**
	 * Returns {@code true} if all worker threads are currently idle. An idle worker
	 * is one that cannot obtain a task to execute because none are available to
	 * steal from other threads, and there are no pending submissions to the pool.
	 * This method is conservative; it might not return {@code true} immediately
	 * upon idleness of all threads, but will eventually become true if threads
	 * remain inactive.
	 *
	 * @return {@code true} if all threads are currently idle
	 */
	public boolean isQuiescent() {
		for (;;) {
			long c = ctl;
			int md = mode, pc = md & SMASK;
			int tc = pc + (short) (c >>> TC_SHIFT);
			int rc = pc + (int) (c >> RC_SHIFT);
			if ((md & (STOP | TERMINATED)) != 0)
				return true;
			else if (rc > 0)
				return false;
			else {
				WorkQueue[] ws;
				WorkQueue v;
				if ((ws = workQueues) != null) {
					for (int i = 1; i < ws.length; i += 2) {
						if ((v = ws[i]) != null) {
							if ((v.source & QUIET) == 0)
								return false;
							--tc;
						}
					}
				}
				if (tc == 0 && ctl == c)
					return true;
			}
		}
	}

	/**
	 * Returns an estimate of the total number of tasks stolen from one thread's
	 * work queue by another. The reported value underestimates the actual total
	 * number of steals when the pool is not quiescent. This value may be useful for
	 * monitoring and tuning fork/join programs: in general, steal counts should be
	 * high enough to keep threads busy, but low enough to avoid overhead and
	 * contention across threads.
	 *
	 * @return the number of steals
	 */
	public long getStealCount() {
		long count = stealCount;
		WorkQueue[] ws;
		WorkQueue w;
		if ((ws = workQueues) != null) {
			for (int i = 1; i < ws.length; i += 2) {
				if ((w = ws[i]) != null)
					count += (long) w.nsteals & 0xffffffffL;
			}
		}
		return count;
	}

	/**
	 * Returns an estimate of the total number of tasks currently held in queues by
	 * worker threads (but not including tasks submitted to the pool that have not
	 * begun executing). This value is only an approximation, obtained by iterating
	 * across all threads in the pool. This method may be useful for tuning task
	 * granularities.
	 *
	 * @return the number of queued tasks
	 */
	public long getQueuedTaskCount() {
		long count = 0;
		WorkQueue[] ws;
		WorkQueue w;
		if ((ws = workQueues) != null) {
			for (int i = 1; i < ws.length; i += 2) {
				if ((w = ws[i]) != null)
					count += w.queueSize();
			}
		}
		return count;
	}

	/**
	 * Returns an estimate of the number of tasks submitted to this pool that have
	 * not yet begun executing. This method may take time proportional to the number
	 * of submissions.
	 *
	 * @return the number of queued submissions
	 */
	public int getQueuedSubmissionCount() {
		int count = 0;
		WorkQueue[] ws;
		WorkQueue w;
		if ((ws = workQueues) != null) {
			for (int i = 0; i < ws.length; i += 2) {
				if ((w = ws[i]) != null)
					count += w.queueSize();
			}
		}
		return count;
	}

	/**
	 * Returns {@code true} if there are any tasks submitted to this pool that have
	 * not yet begun executing.
	 *
	 * @return {@code true} if there are any queued submissions
	 */
	public boolean hasQueuedSubmissions() {
		WorkQueue[] ws;
		WorkQueue w;
		if ((ws = workQueues) != null) {
			for (int i = 0; i < ws.length; i += 2) {
				if ((w = ws[i]) != null && !w.isEmpty())
					return true;
			}
		}
		return false;
	}

	/**
	 * Removes and returns the next unexecuted submission if one is available. This
	 * method may be useful in extensions to this class that re-assign work in
	 * systems with multiple pools.
	 *
	 * @return the next submission, or {@code null} if none
	 */
	protected ForkJoinTask<?> pollSubmission() {
		return pollScan(true);
	}

	/**
	 * Removes all available unexecuted submitted and forked tasks from scheduling
	 * queues and adds them to the given collection, without altering their
	 * execution status. These may include artificially generated or wrapped tasks.
	 * This method is designed to be invoked only when the pool is known to be
	 * quiescent. Invocations at other times may not remove all tasks. A failure
	 * encountered while attempting to add elements to collection {@code c} may
	 * result in elements being in neither, either or both collections when the
	 * associated exception is thrown. The behavior of this operation is undefined
	 * if the specified collection is modified while the operation is in progress.
	 *
	 * @param c the collection to transfer elements into
	 * @return the number of elements transferred
	 */
	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
		int count = 0;
		WorkQueue[] ws;
		WorkQueue w;
		ForkJoinTask<?> t;
		if ((ws = workQueues) != null) {
			for (int i = 0; i < ws.length; ++i) {
				if ((w = ws[i]) != null) {
					while ((t = w.poll()) != null) {
						c.add(t);
						++count;
					}
				}
			}
		}
		return count;
	}

	/**
	 * Returns a string identifying this pool, as well as its state, including
	 * indications of run state, parallelism level, and worker and task counts.
	 *
	 * @return a string identifying this pool, as well as its state
	 */
	public String toString() {
		// Use a single pass through workQueues to collect counts
		long qt = 0L, qs = 0L;
		int rc = 0;
		long st = stealCount;
		WorkQueue[] ws;
		WorkQueue w;
		if ((ws = workQueues) != null) {
			for (int i = 0; i < ws.length; ++i) {
				if ((w = ws[i]) != null) {
					int size = w.queueSize();
					if ((i & 1) == 0)
						qs += size;
					else {
						qt += size;
						st += (long) w.nsteals & 0xffffffffL;
						if (w.isApparentlyUnblocked())
							++rc;
					}
				}
			}
		}

		int md = mode;
		int pc = (md & SMASK);
		long c = ctl;
		int tc = pc + (short) (c >>> TC_SHIFT);
		int ac = pc + (int) (c >> RC_SHIFT);
		if (ac < 0) // ignore transient negative
			ac = 0;
		String level = ((md & TERMINATED) != 0 ? "Terminated" : (md & STOP) != 0 ? "Terminating" : (md & SHUTDOWN) != 0 ? "Shutting down" : "Running");
		return super.toString() + "[" + level + ", parallelism = " + pc + ", size = " + tc + ", active = " + ac + ", running = " + rc + ", steals = " + st
				+ ", tasks = " + qt + ", submissions = " + qs + "]";
	}

	/**
	 * Possibly initiates an orderly shutdown in which previously submitted tasks
	 * are executed, but no new tasks will be accepted. Invocation has no effect on
	 * execution state if this is the {@link #commonPool()}, and no additional
	 * effect if already shut down. Tasks that are in the process of being submitted
	 * concurrently during the course of this method may or may not be rejected.
	 *
	 * @throws SecurityException if a security manager exists and the caller is not
	 *                           permitted to modify threads because it does not
	 *                           hold
	 *                           {@link java.lang.RuntimePermission}{@code ("modifyThread")}
	 */
	public void shutdown() {
		checkPermission();
		tryTerminate(false, true);
	}

	/**
	 * Possibly attempts to cancel and/or stop all tasks, and reject all
	 * subsequently submitted tasks. Invocation has no effect on execution state if
	 * this is the {@link #commonPool()}, and no additional effect if already shut
	 * down. Otherwise, tasks that are in the process of being submitted or executed
	 * concurrently during the course of this method may or may not be rejected.
	 * This method cancels both existing and unexecuted tasks, in order to permit
	 * termination in the presence of task dependencies. So the method always
	 * returns an empty list (unlike the case for some other Executors).
	 *
	 * @return an empty list
	 * @throws SecurityException if a security manager exists and the caller is not
	 *                           permitted to modify threads because it does not
	 *                           hold
	 *                           {@link java.lang.RuntimePermission}{@code ("modifyThread")}
	 */
	public List<Runnable> shutdownNow() {
		checkPermission();
		tryTerminate(true, true);
		return Collections.emptyList();
	}

	/**
	 * Returns {@code true} if all tasks have completed following shut down.
	 *
	 * @return {@code true} if all tasks have completed following shut down
	 */
	public boolean isTerminated() {
		return (mode & TERMINATED) != 0;
	}

	/**
	 * Returns {@code true} if the process of termination has commenced but not yet
	 * completed. This method may be useful for debugging. A return of {@code true}
	 * reported a sufficient period after shutdown may indicate that submitted tasks
	 * have ignored or suppressed interruption, or are waiting for I/O, causing this
	 * executor not to properly terminate. (See the advisory notes for class
	 * {@link ForkJoinTask} stating that tasks should not normally entail blocking
	 * operations. But if they do, they must abort them on interrupt.)
	 *
	 * @return {@code true} if terminating but not yet terminated
	 */
	public boolean isTerminating() {
		int md = mode;
		return (md & STOP) != 0 && (md & TERMINATED) == 0;
	}

	/**
	 * Returns {@code true} if this pool has been shut down.
	 *
	 * @return {@code true} if this pool has been shut down
	 */
	public boolean isShutdown() {
		return (mode & SHUTDOWN) != 0;
	}

	/**
	 * Blocks until all tasks have completed execution after a shutdown request, or
	 * the timeout occurs, or the current thread is interrupted, whichever happens
	 * first. Because the {@link #commonPool()} never terminates until program
	 * shutdown, when applied to the common pool, this method is equivalent to
	 * {@link #awaitQuiescence(long, TimeUnit)} but always returns {@code false}.
	 *
	 * @param timeout the maximum time to wait
	 * @param unit    the time unit of the timeout argument
	 * @return {@code true} if this executor terminated and {@code false} if the
	 *         timeout elapsed before termination
	 * @throws InterruptedException if interrupted while waiting
	 */
	public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException {
		if (Thread.interrupted())
			throw new InterruptedException();
		if (this == common) {
			awaitQuiescence(timeout, unit);
			return false;
		}
		long nanos = unit.toNanos(timeout);
		if (isTerminated())
			return true;
		if (nanos <= 0L)
			return false;
		long deadline = System.nanoTime() + nanos;
		synchronized (this) {
			for (;;) {
				if (isTerminated())
					return true;
				if (nanos <= 0L)
					return false;
				long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
				wait(millis > 0L ? millis : 1L);
				nanos = deadline - System.nanoTime();
			}
		}
	}

	/**
	 * If called by a ForkJoinTask operating in this pool, equivalent in effect to
	 * {@link ForkJoinTask#helpQuiesce}. Otherwise, waits and/or attempts to assist
	 * performing tasks until this pool {@link #isQuiescent} or the indicated
	 * timeout elapses.
	 *
	 * @param timeout the maximum time to wait
	 * @param unit    the time unit of the timeout argument
	 * @return {@code true} if quiescent; {@code false} if the timeout elapsed.
	 */
	public boolean awaitQuiescence(long timeout, TimeUnit unit) {
		long nanos = unit.toNanos(timeout);
		ForkJoinWorkerThread wt;
		Thread thread = Thread.currentThread();
		if ((thread instanceof ForkJoinWorkerThread) && (wt = (ForkJoinWorkerThread) thread).pool == this) {
			helpQuiescePool(wt.workQueue);
			return true;
		} else {
			for (long startTime = System.nanoTime();;) {
				ForkJoinTask<?> t;
				if ((t = pollScan(false)) != null)
					t.doExec();
				else if (isQuiescent())
					return true;
				else if ((System.nanoTime() - startTime) > nanos)
					return false;
				else
					Thread.yield(); // cannot block
			}
		}
	}

	/**
	 * Waits and/or attempts to assist performing tasks indefinitely until the
	 * {@link #commonPool()} {@link #isQuiescent}.
	 */
	static void quiesceCommonPool() {
		common.awaitQuiescence(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
	}

	/**
	 * Interface for extending managed parallelism for tasks running in
	 * {@link ForkJoinPool}s.
	 *
	 * <p>
	 * A {@code ManagedBlocker} provides two methods. Method {@link #isReleasable}
	 * must return {@code true} if blocking is not necessary. Method {@link #block}
	 * blocks the current thread if necessary (perhaps internally invoking
	 * {@code isReleasable} before actually blocking). These actions are performed
	 * by any thread invoking {@link ForkJoinPool#managedBlock(ManagedBlocker)}. The
	 * unusual methods in this API accommodate synchronizers that may, but don't
	 * usually, block for long periods. Similarly, they allow more efficient
	 * internal handling of cases in which additional workers may be, but usually
	 * are not, needed to ensure sufficient parallelism. Toward this end,
	 * implementations of method {@code isReleasable} must be amenable to repeated
	 * invocation.
	 *
	 * <p>
	 * For example, here is a ManagedBlocker based on a ReentrantLock:
	 * 
	 * <pre> {@code
	 * class ManagedLocker implements ManagedBlocker {
	 * 	final ReentrantLock lock;
	 * 	boolean hasLock = false;
	 * 
	 * 	ManagedLocker(ReentrantLock lock) {
	 * 		this.lock = lock;
	 * 	}
	 * 
	 * 	public boolean block() {
	 * 		if (!hasLock)
	 * 			lock.lock();
	 * 		return true;
	 * 	}
	 * 
	 * 	public boolean isReleasable() {
	 * 		return hasLock || (hasLock = lock.tryLock());
	 * 	}
	 * }
	 * }</pre>
	 *
	 * <p>
	 * Here is a class that possibly blocks waiting for an item on a given queue:
	 * 
	 * <pre> {@code
	 * class QueueTaker<E> implements ManagedBlocker {
	 * 	final BlockingQueue<E> queue;
	 * 	volatile E item = null;
	 * 
	 * 	QueueTaker(BlockingQueue<E> q) {
	 * 		this.queue = q;
	 * 	}
	 * 
	 * 	public boolean block() throws InterruptedException {
	 * 		if (item == null)
	 * 			item = queue.take();
	 * 		return true;
	 * 	}
	 * 
	 * 	public boolean isReleasable() {
	 * 		return item != null || (item = queue.poll()) != null;
	 * 	}
	 * 
	 * 	public E getItem() { // call after pool.managedBlock completes
	 * 		return item;
	 * 	}
	 * }
	 * }</pre>
	 */
	public static interface ManagedBlocker {
		/**
		 * Possibly blocks the current thread, for example waiting for a lock or
		 * condition.
		 *
		 * @return {@code true} if no additional blocking is necessary (i.e., if
		 *         isReleasable would return true)
		 * @throws InterruptedException if interrupted while waiting (the method is not
		 *                              required to do so, but is allowed to)
		 */
		boolean block() throws InterruptedException;

		/**
		 * Returns {@code true} if blocking is unnecessary.
		 * 
		 * @return {@code true} if blocking is unnecessary
		 */
		boolean isReleasable();
	}

	/**
	 * Runs the given possibly blocking task. When
	 * {@linkplain ForkJoinTask#inForkJoinPool() running in a ForkJoinPool}, this
	 * method possibly arranges for a spare thread to be activated if necessary to
	 * ensure sufficient parallelism while the current thread is blocked in
	 * {@link ManagedBlocker#block blocker.block()}.
	 *
	 * <p>
	 * This method repeatedly calls {@code blocker.isReleasable()} and
	 * {@code blocker.block()} until either method returns {@code true}. Every call
	 * to {@code blocker.block()} is preceded by a call to
	 * {@code blocker.isReleasable()} that returned {@code false}.
	 *
	 * <p>
	 * If not running in a ForkJoinPool, this method is behaviorally equivalent to
	 * 
	 * <pre> {@code
	 * while (!blocker.isReleasable())
	 * 	if (blocker.block())
	 * 		break;
	 * }</pre>
	 *
	 * If running in a ForkJoinPool, the pool may first be expanded to ensure
	 * sufficient parallelism available during the call to {@code blocker.block()}.
	 *
	 * @param blocker the blocker task
	 * @throws InterruptedException if {@code blocker.block()} did so
	 */
	public static void managedBlock(ManagedBlocker blocker) throws InterruptedException {
		ForkJoinPool p;
		ForkJoinWorkerThread wt;
		WorkQueue w;
		Thread t = Thread.currentThread();
		if ((t instanceof ForkJoinWorkerThread) && (p = (wt = (ForkJoinWorkerThread) t).pool) != null && (w = wt.workQueue) != null) {
			int block;
			while (!blocker.isReleasable()) {
				if ((block = p.tryCompensate(w)) != 0) {
					try {
						do {
						} while (!blocker.isReleasable() && !blocker.block());
					} finally {
						U.getAndAddLong(p, CTL, (block > 0) ? RC_UNIT : 0L);
					}
					break;
				}
			}
		} else {
			do {
			} while (!blocker.isReleasable() && !blocker.block());
		}
	}

	/**
	 * If the given executor is a ForkJoinPool, poll and execute
	 * AsynchronousCompletionTasks from worker's queue until none are available or
	 * blocker is released.
	 */
	static void helpAsyncBlocker(Executor e, ManagedBlocker blocker) {
		if (blocker != null && (e instanceof ForkJoinPool)) {
			WorkQueue w;
			ForkJoinWorkerThread wt;
			WorkQueue[] ws;
			int r, n;
			ForkJoinPool p = (ForkJoinPool) e;
			Thread thread = Thread.currentThread();
			if (thread instanceof ForkJoinWorkerThread && (wt = (ForkJoinWorkerThread) thread).pool == p)
				w = wt.workQueue;
			else if ((r = TLRandom.getProbe()) != 0 && (ws = p.workQueues) != null && (n = ws.length) > 0)
				w = ws[(n - 1) & r & SQMASK];
			else
				w = null;
			if (w != null) {
				for (;;) {
					int b = w.base, s = w.top, d, al;
					ForkJoinTask<?>[] a;
					if ((a = w.array) != null && (d = b - s) < 0 && (al = a.length) > 0) {
						int index = (al - 1) & b;
						long offset = ((long) index << ASHIFT) + ABASE;
						ForkJoinTask<?> t = (ForkJoinTask<?>) U.getObjectVolatile(a, offset);
						if (blocker.isReleasable())
							break;
						else if (b++ == w.base) {
							if (t == null) {
								if (d == -1)
									break;
							} else if (!(t instanceof CompletableFuture.AsynchronousCompletionTask))
								break;
							else if (U.compareAndSwapObject(a, offset, t, null)) {
								w.base = b;
								t.doExec();
							}
						}
					} else
						break;
				}
			}
		}
	}

	// AbstractExecutorService overrides. These rely on undocumented
	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
	// implement RunnableFuture.

	protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
		return new ForkJoinTask.AdaptedRunnable<T>(runnable, value);
	}

	protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
		return new ForkJoinTask.AdaptedCallable<T>(callable);
	}

	// Unsafe mechanics
	private static final IUnsafe U = UnsafeAccess.unsafe;
	private static final long CTL;
	private static final long MODE;
	private static final int ABASE;
	private static final int ASHIFT;

	static {
		try {
			CTL = U.objectFieldOffset(ForkJoinPool.class.getDeclaredField("ctl"));
			MODE = U.objectFieldOffset(ForkJoinPool.class.getDeclaredField("mode"));
			ABASE = U.arrayBaseOffset(ForkJoinTask[].class);
			int scale = U.arrayIndexScale(ForkJoinTask[].class);
			if ((scale & (scale - 1)) != 0)
				throw new ExceptionInInitializerError("array index scale not a power of two");
			ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
		} catch (Exception e) {
			throw new ExceptionInInitializerError(e);
		}

		// Reduce the risk of rare disastrous classloading in first call to
		// LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773
		@SuppressWarnings("unused")
		Class<?> ensureLoaded = LockSupport.class;

		int commonMaxSpares = DEFAULT_COMMON_MAX_SPARES;
		try {
			String p = System.getProperty("java.util.concurrent.ForkJoinPool.common.maximumSpares");
			if (p != null)
				commonMaxSpares = Integer.parseInt(p);
		} catch (Exception ignore) {
		}
		COMMON_MAX_SPARES = commonMaxSpares;

		defaultForkJoinWorkerThreadFactory = new DefaultForkJoinWorkerThreadFactory();
		modifyThreadPermission = new RuntimePermission("modifyThread");

		common = AccessController.doPrivileged(new PrivilegedAction<ForkJoinPool>() {
			public ForkJoinPool run() {
				return new ForkJoinPool((byte) 0);
			}
		});

		COMMON_PARALLELISM = Math.max(common.mode & SMASK, 1);
	}

	/**
	 * Factory for innocuous worker threads.
	 */
	private static final class InnocuousForkJoinWorkerThreadFactory implements ForkJoinWorkerThreadFactory {

		/**
		 * An ACC to restrict permissions for the factory itself. The constructed
		 * workers have no permissions set.
		 */
		private static final AccessControlContext ACC = contextWithPermissions(modifyThreadPermission,
				new RuntimePermission("enableContextClassLoaderOverride"), new RuntimePermission("modifyThreadGroup"), new RuntimePermission("getClassLoader"),
				new RuntimePermission("setContextClassLoader"));

		public final ForkJoinWorkerThread newThread(ForkJoinPool pool) {
			return AccessController.doPrivileged(new PrivilegedAction<ForkJoinWorkerThread>() {
				public ForkJoinWorkerThread run() {
					return new ForkJoinWorkerThread.InnocuousForkJoinWorkerThread(pool);
				}
			}, ACC);
		}
	}
}
